Testors enamel work well with Silmar41. I haven't tried the acrylcs. You will have to experiment with what level of opaqueness you are looking for, although Gerry's amount is about right, as I use less, but I am only coloring about 3.5 ounces of resin at a time.
Note, you can get a 9 pack of enamels (actually 8 colors (red,blue, green, yellow, white,black,gold, silver and 1 thinner) at Michaels, use one of their 40-50% coupons and it will be about $5-6
You can mix in Pearlex Micro or Macro Pearl to add pearlescent to the colors. (not sure what these are called in Coastal Scents products). Works great.