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For the workshop you will need three primary colors of fluid acrylics.
Any RED Any Blue and Any Yellow. You can be safe and buy the ones that say Primary or branch out. You will also need to have some colors that are closely matching your image colors. Maybe another three choices.
The One Ounce bottles are small and the Eight Ounce bottles might be too much paint. My suggestion is to buy a “set” like I recommend and that will be your primaries plus more and then add a few small one ounce bottles of your painting colors.
I highly recommend GOLDEN acrylics instead of anything that is a lower priced “craft” paint. The reason is the pigment in professional paint is much higher and that means you not only use LESS paint but you get a more brilliant and purer color. Craft paints also are not mean to always mix with gel mediums. I have happily played with craft level paints in other projects but never for fine art applications.
So a SUGGESTION for three colors (for instance):
Alizarin crimson or quinacridone rose
Hansa Yellow medium
You can download a Color Chart for What colors are available HERE