Making comics is making art, and art often (if not always) involves a number of aesthetic choices.
Comics, going back to the era of traditional print media, have frequently been printed in black & white or shades of grey. As an artist you may never consider taking beautifully coloured comics and posting them in greyscale… or, just perhaps, you’ll make a creative decision (as I have) to call back to traditional three-panel strips and use a desaturated palette.
In that case you may someday need an easy way to flip back and forth between colour and greyscale art, objects, and models and it’s not entirely obvious the best way to do this in Inkscape 0.91.
Getting Started
Let’s say, for sake of example, you have a bit of art that you’ve created in Inkscape (in color) that you want to turn into a black and white image for use in a non-color strip.

While there are plenty of ways you can do this (hand colouring objects, using extensions, exporting in color and desaturating in another piece of software) there is a simple way inside Inkscape that (a) is quick and consistent and (b) allows you to re-colourize your art at a later date.
Filters > Color > Greyscale
Of course, you’re going to want to select the object(s) that you want to convert to greyscale before reaching into the filter menu. In this case, using a filter is powerful choice because as you’ll see in a later step, you’re not actually changing or removing the colours, but on a per-object basis masking it into a different mode.
In fact, if you were to open up your SVG file in a text editor and look at the objects that make up your art (and you can actually do this) you’d see that after applying a filter, the colours are all still there but there is an added property attached: a filter code. This filter code essentially tells the software to turn that colour into a shades of grey based on the settings you see in the next dialog box.

Choosing Filters > Color > Greyscale
is going to present you with some knobs to twiddle.
Feel free to adjust to your personal aesthetic, but for my purposes I’ve generally found the defaults to work pretty good.
Then, press Apply
.

The result is that the object to which you’ve applied your filter is now on screen (and if you’re exporting it later) in black and white (or specifically, in greyscale… which is 256 shades of black or white).
Here you can tweak colors, adjust colors (all in greyscale of course) and continue working on your art … which is the important part.
You’re not branching your art into two different sets of models.
If you’re the type of artist that works from a library of reference art, you want models that you can re-use, edit later, anywhere and everywhere. In this case, permanently creating a set of art that uses a different colour palette is a waste of time and leads to the chance of character inconsistencies…. but most importantly wastes time. Did I already mention that? Oh well, it’s so important that it’s worth mentioning twice. Stop wasting time.
In this example, my magpie is a character that appears frequently in some comics. In fact, there are three magpie characters that I use (it’s subtle, but it’s my thing!) and each are differentiated by the slightly different palette used for their wing feather highlight.
If I do some work on this guy now and decide I want to convert him back to a full colour model, maybe because I decide I want to use this model later on in a full-colour comic, then I don’t want to muss around with trying to go through my art object by object and color-matching everything. I just want him back in beautiful full colour so I can get back to drawing.

So, how do I convert it back to a full colour model?
If you’ve used the filter, it’s actually quite fast and simple:
Filters > Remove Filters
After all (and as I will repeat so often in these articles you’re going to be sick of reading it) as a piece of vector art your drawing is just math. By adding the filter you never actually removed the color, changed the color, or altered the palette. (You may have done that in tweaking afterwards, but that’s a whole different article.) As written above, you’ve just added more math: a bit of extra code to that makes up that calculation that is your art objects. This command reaches into each selected object and punts that bit of added math (ie the filter code) to the curb. No more filter, no more greyscale.
So… simply remove the greyscale filter:

The result is that you’re back to where you started (as far as colours at least).
Draw on my little magpies, draw on…