I took my 2015 IS250 F Sport in because the rear brakes was squeaking. Only 4,600 miles. Service advisor left me a message that they replace the brake caliber. Now the brake caliber is two different colors! Can someone tell from the picture which brake caliber this is? I'm not happy because I don't want my car to look like its mix and match. Thinking of taking it back to get my original brake caliber installed back (that's if they kept it).

 

*caliper
Yes there is bulletin about rear brakes on IS250.
If they stated they replaced the caliper only then most likely it doesn't match because the caliper bracket is the same one on your car and wasn't replaced because it wasn't the trouble part. Color difference is due to different manufacturing time or factory than the original.
Your original caliper removed was probably sent back to corporate for inspection.