kinda looks like mosaic virus to me, but i've been wrong before

What species of plant are the leaves from?

Looks like leaflets from a variegated Schefflera arboricola.

If it is a variegated Schefflera arboricola (and I agree, it probably is), the variegation is due to a chimera. Variegation caused by a virus is generally not distinctively two-toned (like the variegation shown in the picture above) and are usually more splotchy (shapes of affected area are different).

Thank you! And you're both right: it is an umbrella plant (S. arboricola). I'm glad it's not infected so I don't have to worry about spreading a virus, and I've always found chimerism fascinating, especially in cases like this.

Wouldn't it be easy to test for a virus by trying to spread the suspected infection to an unvariegated plant of the same species and seeing whether it develops variegation? I.e, mash up some variegated leaves and apply to a wound on the unvariegated plant?

Apparently, there are cases of human chimeras composed of cells from nonidentical twins.

If it wasn't fairly easy to determine if a virus was causing variegation by simple observation and a small amount of research, the method of checking to see if the virus would spread might be a useful tool. Proper scientific research methods would need to be followed.