Hi there Molandme and a warm welcome to the Animal & Wildlife Forum!
It's always difficult to decide on a background colour for a dog portrait, isnt it?
Nice dog and you can get lots of texture into his fur with pastels.
Background paper color? I think it depends if you are intending to put the grass in the background or are you just going to leave the background the paper color?
If you are putting the green grass into the background you could go for a pale paper, put your green grass in, then you would also need to use some of the green in the dogs fur to tie the whole portrait together.
If you're not going to put the grass into the background, you could use a blue toned paper as there's blues in the dogs fur. The choice is yours.
Just a note: if you had posted this thread in the main page of this Forum you would have got many more replies. This Sub-Forum is mainly for Projects etc.
As Moderator of this Forum, I can move your thread to the main part of this Forum if you would like me too?