The colour will vary depends on the degree.
For the best range, please choose:
50 degree - for sub 300fps AEGs, and cold weather
60 degree - for 300-330fps
70 degree - for 330-350fps
75 degree - for 340-350fps
80 degree - over 350fps
Included is a 3D printed nub, which is original design (not Maple leaf) that boosts the effect of the concave shape of the rubber. This nub is designed a bit higher than the ordinary cylindrical nub, so you will need less hop up than before. It is made of elastomer (rubber-like plastic) to minimize the risk of piercing the bucking.
Usually, replacing the bucking and the nub is not hard, but make sure the nub does not press the bucking too much as it will jam the bbs or too close to the edge of the barrel window as this may shear the wall of the bucking!
If you are buying nubs only and you purchase 2, you will get +1 free.
Please, look at my positive feedback and buy with confidence.