Cernit offer pure primary mixer colours in the larger 500g blocks only - this is 717 Primary Yellow - a brighter, cooler yellow than their regular shade, more akin to the zinc yellows now discontinued from so many brands.
Primaries are designed specifically with colour mixing in mind and are 50% opacity colours. This means they have a more translucent finish for a porcelain-like depth to the baked clay and the colours will appear darker and more intense accordingly. To lighten colours and maintain this finish, use the Porcelain white. To lighten colours and also make them more opaque, mix with the opaque white.
Cernit polymer clay Number One range has a wide selection of colours and is Phthalate-free. It is easy to use and very strong when baked, even in thin sheets. Bake for half an hour at 110 - 130 degrees C.