Why is my daughter's abdomen tinted green?

That matches up fairly well. There is not a lot of color in that bathroom. The walls are light blue and the ceiling is white.

This sounds reasonable.

Maybe just semantics, but I don’t know if I would call it a “trick.” The greener light is there. I can take a picture of it, and open it in a photo editing program, those regions have a higher green component.

The most likely thing is unrecognized cirhhosis with prominence of the subcutaneous veins over the abdomen… not…

She probably just has very pale skin. If it really does look green, it’s just an effect of the ambient lighting along with bluish subQ veins plus a thin layer of yellow subcutaneous fat.

That happened to me when I ate too many black jelly beans!

I second that it may be clothing dye, or distorted color perception from a light bulb.

Also, the skin can take on a different appearance in bath water, due to the water filtering the light, and refraction through it and bouncing off the tub walls. This could be amplifying any effect the fluorescent lights may be producing, which as noted already, produce an unnaturally greenish-white quality of light.