One thing I miss from the light level indicator in prior versions (1,7.10 and earlier) where the green/yellow/red X markers. I liked this for several reasons -

1 - It didn't feel as obtrusive (the numbers are thick and take up the entire block - making it harder to see the terrain I'm working with).
2 - Yellow X's indicated blocks that were open to the sunlight, which was good if I wanted to light some of the outside, and there was an area with red X's there were say, under an overhang.
3 - Related to the first one, I didn't see the overlay where I had torch light, making it less confusing to find a red or yellow X that I missed.

Perhaps add an extra key (F5?), or F4 could cycle through several modes of overlays, one being raw light level, and the other being "skylight level".

Currently you can use Shift + F4 to switch between "Torch Light Only" and "Torch Light + Sky Light" mode. I will consider to add a "Mixed" mode contains yellow numbers in next release.
And for X markers, you can use a resource pack to change the numbers to X markers.

Added yellow numbers in advanced mode. For details, please check the change log: http://minecraft.curseforge.com/projects/light-level-overlay-reloaded/files/2312553