First I’ll start with the thoughts that have already occurred on here.
I disagree with Cyanocephalus and Hartzfeldii, if we’re assuming this is a mature male at 4 inches then the colours on these two are completely different as mature males.
Now, Zeylonicus as an adult is a gorgeous green/orange colour pattern. Your specimen is a white with a brown stripe before the dorsal. Again, Pelicieri is a close match as juvenile but the bar is lower down than your specimen shows. As for an adult Pelicieri they’re more greens and black. Bleekeri as a mature male is orange and green/blue.
To find a definite ID the best thing is to look through each genus that has species with similar features. So for this you want to look into the
Coris genus as well as
Halichoeres.
The main ones that come up are;
Coris venusta
Coris dorsomacula
Coris caudimacula
My vote goes to a transitioning male
Coris dorsomacula. After looking into the photos closely I can see not only the dorsal stripe bars but also two deep lines on the body which look very similar to this guy. You can also see all 3 fins (Dorsal, Caudal and Anal) starting to gain more colour and look close to the male on the photo below - not my photo.
I will admit this stumped me for a while because I wasn’t looking outside the box and was trying to find
Halichoeres species that match this guy.