The bug

The handle of levers is shaded and appears darker than the texture would imply. This effect was first introduced in 14w10a, and was noted in MC-50274 (said ticket listed two things, but was only marked as a duplicate of one of them). From Alpha v1.0.1 to 14w08a, the lever handle did not have this shading.

I am not sure if the current lever appearance is now considered the intended appearance.

How to fix

This can be easily fixed by adding

"shade": false"

to the handle element in models/block/lever.json and models/block/lever_on.json. Fixed model files are attached which build upon the fixes for MC-262631 and MC-262864. This fix should therefore be no more difficult than dragging and dropping these files into the block model directory and replacing the existing ones.