Turtle

a red ear slider's shell is a lighter color of green to dark green with yellowish patterns, the carapace is weakly keeled and has a slightly serrated scutes on its posterior of its shell. The painted turtle's shell is olive to black with some red markings coming up onto the carapace and will sometimes have a red stripe going down the spine of the shell (depending on what variety of painted turtle).

is the carapace slightly more domed than a red eared slider?What is the major distinguishing factor besides the red ears of course!

The carapace looks like a painted turtle, red ear sliders have yellowish markings on their carapace. Also there are red stripes on the fore limbs and red ear sliders do not have red stripes on their legs but yellowish stripes.

Red eared slider, looks like - Trachemys scripta.