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!