Just to clarify, the cuttlefish video is not an entirely accurate representation of slime abilities. Slimes can shapeshift the shape and percieved size of their forms, which does not affect camouflage at all. They can also change colours, but this ability was not intended in the spirit of camouflage - the bestiary specifies "For instance, a Slime that is very cold might turn blue."

Slimes in their default state would not be able to either change colour to camouflage - rather, they could change into different solid colours or gradients, and on command rather than as an emotional reaction only with practice. They also are "semitransparent," not transparent, and as such would not be able to fully blend in to their backgrounds in that way.

With that said, a textural shifting ability would be absolutely okay as a tier one reward. If this is still something you are interested in with the above clarification, you may consider this ability approved!