Any color with blue or green in it in the air dry line of paints will need to be pretty thinned with your diluting products as these colors grab to the vinyl very intensely and do not let go. When air dry babies fade, it is the blues that will remain because they don’t fade and then the baby looks dead. When thinning any red based color you want to be sure you are using a diluting product with binders in it and not just water. Examples would be flow medium, matte medium, matte gels, glaze medium etc. You can pick your choice based on what you like best. Do not add more than 30% distilled water for best results. You can then pounce your mottle sponge on a paper towel first so as to not apply the colors too heavily. As for the purples, they are a mix of red and blues so you want to thin them down to thin the blue but keep in mind the balance of not having the red in the mix fade out. Quite honestly, this is the reason I left air dry painting. It takes a lot of work to make sure your colors are thinned properly and do not fade and fighting the constant sheen of the mediums. The most matte medium is the Liquitex Ultra Matte Gel. The best thinner IMO is Jo Sonjas flow medium or Glaze Medium. Both are more watery. Flow medium is best for painting hair. I mixed them with the Ultra Matte Gel to combat the sheen when I was using air dry. Golden Fluid Paints I found to be the best at holding pigment strength when thinned down.