I was born in 1997, and this is a book meant for preschool to kindergarten kids. I’m guessing it’s a late 90s (maybe earlier) or early 2000s book.
I can’t remember the cover well but I believe the dog was like a terrier, mostly whitish with maybe a spot or some brown fur. In the short picture book, each page is dedicated to a color and the dog then wears clothes matching and does an activity matching as well. I remember for yellow he wore a yellow raincoat and for purple I think there was some purple grape jam involved. I want to say for the color black the dog appeared as a mime maybe? I remember black and white stripes. I believe the plot involved trying to decide what his favorite color was.
The style used for the illustrations was unique, the pictures were simple and used minimal detail. I want to say they were a type of watercolor, the children’s book “Where’s Your Creativity?” is drawn in a similar style but it’s not quite it. I included a picture. Wishing you luck, thanks!
Perhaps ‘Dog’s Colourful Day’ by Emma Dodds? Published 2001 New York, also 2002 London, Puffin
Unfortunately not that one, but thank you for trying!
‘Kipper’s Book of Colors’ by Mike Inkpen? Pub 1995.
Terrier-like dog, a shadow rather than mime, however it only fits your desciption vaguely…