There are some pure water-colourists out there who have very hard and fast rules about what you should and shouldn't use. My personal opinion is you should use whatever you like, to achieve the paintings you want to paint . If you impose limits on yourself or prefer not to do things,then I think that is entirely up to you . I have some things which I prefer not to do. One of those things is use black ( I never say never ) but I very very rarely use black, and few watercolour artists do. So much so that I get annoyed when it is included in a set of paints. Black as a colour is a flat dead colour and it seems to deaden a painting ( in my opinion) , so what do you do when you are painting something black?
If it is a small thing , like the dark areas in this kingfisher's eye
then I use a mixture of sepia ( a very dark brown) and indigo ( a very dark blue) . Then I have a 'black', why not use black then ( I hear you cry). I don't know but this just feels right and looks better. Use any blue and brown mix to give yourself a grey or black dark colour, and I like to place a dark next to a light so they both stand out.
So what about something like a badger, that's black and white right? Well no I have found the more I paint the more I realise things are seldom that simple.For large amounts of black I use paynes grey
Paynes Grey does have black in it but also blue, and when painting black fur if you study it closely it reflects back the light , so I pop cerulean blue in there and purple. I also add watermarks to add interest, just as the black isn't black the white isn't white there are all sorts of shadows in it.
I did similar things when painting these magpies
You want the translucency of the wings to shine through.
Also with my zebras, the more colours the better.
So how to tackle a completely black dog? In much the same way look for the colours and the contrasts. You need to paint what you see not what you think is there .So if the fur is reflecting back blues or purples or even greens, be brave and pop them in.I use Paynes Grey again as my black but I want contrast and interest so I need to add colours and shadows
So in some places the black dog is almost white.
I like to do the same with my bees, just plain black would look flat and uninteresting, there are browns, blues, and purples in amongst the black .
Cerulean blue is the colour I most use as a highlight in black areas
When I want a black or dark background to contrast against a light subject then I use my trusty Paynes Grey again,
I try to put the darkest tones next to the lightest areas, then I go crazy with water, paint and salt or splashes and flicks. So my background is interesting and random, have fun!
Finally if I need to paint a shadow ( then they are not black ) I often use a mixture of cobalt blue and cadmium red
but shadows can be blue, grey, green when you are out and about observe them and try to paint what you see
So black is very rarely black , and I find with painting always the more you look then more you see.