Why do we mark tlc plates with pencil and not with pen

Need to answer this question on a discussion board post

Type the correct answer in the box. spell all words correctly. what will steve render color accurately in his photograph? will him render color accurately in photographs, depending on the steve is photographing his kitten on his will him render color accurately in photographs, depending on the light conditions under which he shoots.

Name the primary colors. why are these colors considered the only “primary colors”?