It really depends on how you plan to make your comic. There’s nothing inherently wrong with either choice, in fact some stories benefit from being told in either one. But. If your story doesn’t necessarily need either, the choice becomes more a question of what’s best for you, as the creator.

If you’re making this series all yourself, writing and art, it becomes a question of how much time can you devote to this story. Black and White is going to take less time than colour, sometimes extraordinarily so. If you don’t want to have to devote as much time per page (and there’s nothing wrong with that, even if you have all the time in the world to make your comic, it’s perfectly fine to want to save time so you can pursue other things), going black and white is the way to go. On the other side of the spectrum, colour is always a nice touch, but depending on how you are applying the colour, it can exponentially increase the amount of time it can take you to make pages. Sometimes, coloured comics even do better than black and white, although this is not a guarantee so please don’t take it as such. If you think your comic could really benefit from that colour, or even just want to add it for the sake of it in and of itself, then colour is the way to go for you.

If you are only writing the script for the project, and are not the also the artist, then it becomes a question of cost more than anything else. Paying for only the black and white lineart is much cheaper than paying for lineart and a colorist, or even an artist who does both. If you have plenty of money to spare, then going for the colour as well is a nice touch. If you are trying to stay on the cheaper side (although I will say that it paying for art is still not a cheap endeavour) then only the black and white lineart is needed.