I think that the beauty of painting is that you can add colours that aren't there and use colours that you enjoy using. I think when I started painting I would look at a subject and try to slavishly copy it when actually as long as the painting looks how I want it to look the colours are up to me.
Let me see if I can show you what I mean...often when painting a landscape I will paint the distance in a mixture of cobalt blue and cadmium red (in fact these colours are 2 of my favourites) even if I can see colours in the distance I don't put them there.
It throws the background into the distance and allows the viewer to see the foreground.
When I am painting blacks I like to add some cerelean blue and or purple into them to add light and interest even though you may not be able to see them in reality
I sometimes just like to play around with colour , hedgehogs aren't really purple and silver but I like those colours and they work well for me so away we go. If the finished piece is pleasing then just go with it
And when it comes to backgrounds I use colours that contrast the piece e.g. the seagull against the purple clouds is just completely made up
As is the pink background for the tiger ...
And some times I just add use favourite colours for a bit of zing!!! And because I am the artist and I can do whatever I like
So if you like to paint don't worry too much about the actual colour unless that is what you like to do. You are in control so play around with colours and see what works for you.