gray-card

Only tried this recipe for the first time today and need more mayonnaise and finer crushed cornflakes. Anyway I fine tuned my Spyder software/hardware and worked on the image. It looked much too yellow and orange and I reduced them. The original chicken looked more brown than orange or...

I have a grey-card on my shopping list, but am confused about the differences in their making and their price. Apart from the 18% or 12% question, can I just pick any and be good, or is there something I should consider? Thanks guys!