The Honeywell RU6500 Series is a full facepiece respirator manufactured by Honeywell.

Honeywell offers both tinted and non-tinted lens covers for this respirator. Unfortunately they are only sold in packs of 25 and thus are prohibitively expensive. Though the lens geometry has compound curves, they are very slight and can safely be ignored when applying tint film. The lens is polycarbonate and theoretically can be dyed. Do note that the lens has some sort of protective coating that may need to be removed before dying will work. The manual does not mention what type of coating this is and only references it when advising the user not to use abrasives while cleaning it.

b4412c has tinted one and traced the cut out tint before applying it. The original scan and an svg traced from it can be found here. In theory it should be possible to print out the trace, verify it is to scale, and use it as a template to cut tint. b4412c has also found success using the trace file to 3d print mesh-like inserts that cover the inside of the lens and can be customized. Bring the trace svg into the slicer of your choice and scale it to 97.5% with a thickness equal to two or three layers. Set top and bottom surfaces to 0 and infill density to a high number. Adjust infill pattern and density to taste.