Try this:
-Use the Elliptical Marquee tool to draw a circle on blank layer
-Flood Fill the selection with a color (try not to use white, that way you can colorize the ring later on)
-Go to Selection > Modify > Contract, then contract the selection by however many pixels you want
-Delete the inside of the circle to make a ring
-Colorize the ring which ever color you want (Ctrl + U)
-Duplicate the ring layer and set the blending mode of the new layer to Linear Dodge
-Go to Filter > Blur > Gaussian Blur, blur the new ring layer by about 4 (or more if you need to)
-Keep duplicating the blurred ring layer until its how you need it
It should turn out something like this (remember, you can keep duplicating the blurred ring layer until the color is how you need it):
Hope that helps!!