If you had a royal palm that looked correct and was strickly black and white, not showing a hint of red or brown could it still be hiding something like calico/sweetgrass in it's background?
In a word, No. The deciding gene between Royal Palm (Ermine) and Sweetgrass (Calico) is reccesive, and the RP has it. So, if you have a perfect looking RP, It genetically can't have a 'Sweetgrass gene' hidden in it's genetic makeup.