Oh-Kay... I'm not sure whether you are over thinking this or not; so lets start at the top.
IN FILM.. we talk of 'Black & White' errantly, what we MEAN by B&W is 'pano-chromatic monochrome'... but that's a bit of a mouthful! Basically the stuff 'responds' to the full spectrum of light colours in the rainbow.. but it makes an image that's in digital-speak 'grey-scale'.. a full range of shades but not colours.
The alternative and probably more correct 'Black & White' film, is 'Lithographic' film, which again, tends to respond to the full range of colours in the rainbow, but will only produce 'Black' or 'white' nothing in between... in digital speak a 'line-art' image. Uncommon stuff, mostly used in reporgraphics.. so, like most I shall ignore it for now, but fascinating stuff if you want to read up on it, especially here most commonly used to make 'colour' images from 'separations'... however...
Coloured filters for 'Monochrome' flm photography are usually used as contrast modifiers. They pass their own colour of light, and block all others; hence you get a very strong contrast response; typically yellow, orange or red, used to lighten the white clouds and darken blue skies; yellow having relatively mild effect, orange a bit stronger, red making a fluffy summer sky look like a howling storm!
That is the principle.. want a reverse effect, use the complementary colour filter; so a 'blue' filter would lighten the blue sky and reduce contrast with clouds, a green filter, lightens grass and foliage, etc.
Exposure.... most filters are marked with thier 'Wratten Number'.. basically the number of 'stops' of light that they 'block'.. this is a hangover/throw-back to the olden days.... to some degree....
Lets say, I was using my Grandad's Kodak Retinette, which he so loved using a yellow filter on.... This is a fully clock-work, fully manual camera, with no 'TTL or Through-The-Lens' metering... you assess exposure by F16-Sunny or a hand held meter....
F16-Sunny, from memory is an Exposure Value of EV10.. and would suggest on 100ASA film, I used a shutter of 1/100th @ f16.. If I waved the light meter around, I would probably get anything from EV8 to EV12, depending on whether I was using the it to take an 'incident' reading with the inver-screen over the sensor, or to take a 'reflected' reading without, depending on what I was pointing the thing at.. B-U-T assuming a little nous, and estimate that the sky WAS close on f16-Sunny, I'd dismiss the more wild ones, and go with something 'around' EV10....
BUT.. the FILM isn't gong tp get all that light... if I have the yellow filter on it probably has a Wratten No of 1/2 stop, the orange, maybe 1 stop, the red possibly 2-stops.
SO.. from a hand-held meter or guesstimate of ambient lighting, if I used that exposure suggestion, then the filter would reduce light getting to the film, and my picture would be under-exposed; SO, to compensate, I would 'up' the exposure by as many stops as the Filters Wratten rating; so half a stop for yellow, one a stop for orange and two stops for red.
NOW... if I was shooting the Olympus OM10... full TTL, through-the-lens, coupled 'auto-exposure'... filter on the front of the lens; 'in-camera meter reading, a-n-d... the meter is only measuring the light that gets through the filter.. so the Wratten-Rating is already compensated for... give or take a bit. Make sense?
Lets go widgetal....
Your basic Digital Sensor is naturally Black & White... strangely enough.... or at least pano-chromatc monochrome... the sensor reacts to the light falling on it, whatever colour it is, and delivers a signal, proportional to the brightness... just like mono-chrome film...
This is where the lithographic principles come in; because to make a 'colour' picture, the camera 'sort' of does what they used to in lith-printing, and filter the colour scene, and take a number of 'separations' through different filters to get the colour separations, to composite in reproduction...
The camera's sensor then has a 'honey-comb' array of receptors, that would respond to all colours of light, BUT there's a screen of red-green-blue filters making each idividual receptor responsive to 'only' that colour of light... sampling the signal from adjacent receptors the electrickery can then interpolate the RGB values it ascribes to image pixels in the digital-image file you will eventaually view.
Oh-Kay... put a red flter over the lens of a conventional DSLR... First up, it will usually contain a Through-The-Lens light meter.. so if you have a 2-stop Wratten rating.. it will suggest two stops more exposure for it... Remember, its no different to using a conventional film camera; the Wratten No, really only applies if you are metering the scene before the filter...
ONLY.. now you are fltering ALL the sensors receptors red.. 1/3 of them already are, so they are getting the light they would have any-way... the Green & Blue filtered receptors though, aren't going to get anything, as the red flter has already nicked thier signal (or at least most of it)!
This can then sort of screw the metering.. not so much for the base exposure, but when the electrickey comes to poll the receptors and 'interpolate' the green and blue values, and finds them rather lower than it expects.... this can then sort of fry the electrikeries mind a bit... and it can pull down the values it gets from the red-filtered receptors and boost the blue and green... and it can 'adjust' the overall exposure either way.
Hence, with digital, you are 'best' doing your RGB filteration in the digital domain, in post-process; where you can normally see the separate separation layers for Red/Green/Blue, and rather than using an arbitary B&W reduction, taking the layers individually and compositing to your preferance.. which is probably getting a bit deep, without a demo, using specific software...
But, for eg. In Photo-Shop, you have the option of coverting to grey-scale, and the software sort of averages the RGB values for each pixel to a single 256 Grey-Scale. However, you can adjust the contrast in each colour layer, first, to get more or less red/green/blue filter effect, or copy/past the indivdual seperations into a grey-scale image at whatever transparancy level you preffer....
Make sense?
BUT... the lesson is, because a digtal camera's sensor is already RGB filtered at source; using colour-filters on one as you would for mono-chrome film, DOESN'T really 'work' the same way, or provide the same effect... even if you are shooting in a B&W mode.
B-U-T either way, the Wratten-Rating of any filter is only relevent if you are metering pre-filter; ie with a hand-held meter (or by eye) rather than TTL. (For the most-part.. big-stoppa thick-shake filters, probably beg ther own explanation of the anomolies at that level of filtration, but I wont go there!)
A-N-D shouldn't really matter whether you are using 'square' system filters or round screw-on ones; the principle remains, as far as Wratten-No & Metering go.
I only ask as I took my first medium format photos a few weeks ago using filters and they didn't really work as I hoped. I used a graduated colour filter but it didn't come out as strong as I hoped. 
