Yamaha dealer here carries the white sliders . They don't bother with short and long sliders, they just bring in one length and you cut to fit. White is virgin UHMW and any other slider color is a dye used to change it to that color which changes the molecular structure of the virgin white compound and makes them a little softer and wear faster. I run white sliders or Graphite sliders with Kimpex 135mm spoke wheels. Most idlers , no matter which brand are made at one place , I know the big 4 get them from the same place, as for Excell I don't know where they get theirs made as I have not had one in my hands.
Don't worry about the Kimpex idlers and cheap bearings, 2000 miles on the cheap bearings and still good.. I pop the seal on any bearing before I install it and give them a extra shot of grease. Even the NTN bearings are not left out of this treatment, They have shown very little grease most times and the odd one with no grease so they are not perfect either. Don't overdo the grease , just a little extra is good.