Red Green and Yellow trails are mostly indicative of difficulty. This is especially true in the case in Red trails. But also a "potential for damage" gauge. I would not rate trails on rig size, because I have seen rigs on 33s do things rigs on 44s didnt accomplish! Has not only to do with equipment, but with commitment!
Green are virtually no possibly for damage. Access roads and such. These will never change. I have been all over the SHOP on these in my Comanche. Stock, open-open 3.55 gears with 32" A/Ts
Yellow while not always so difficult, pose a certain chance of damage. Trees, rocks, holes. A lot of hillclimb areas arent so difficult, but have the possibility of body damage, driveline breakages, and of course, in extreme cases, rollover. Also, as these wear in from riding, some may become Red. (I have been on several of these areas in my Comanche. I did stay away from the steeper hillclimbs as this is my DD shop truck!)
Red, of course are the most difficult (except Black). Definite possibility for damage. Body and chassis damage. And driveline breakage. These trails require equipment like lockers, cages, body armor. Winches are expected for recovery and several of these trails have not yet been made all the way through without a winch as of this last workday!
The only Black trail is Razorback. It is recommended for experienced wheelers. It is a very steep, very twisty, very narrow, very long, loose dirt hillclimb. It runs up a ridge or razorback. If you fall off the trail, you are in trouble. Recovery would be very difficult. This trail requires full rollcages and winches. Also recommend a full harness. (It is a very bad hill to have to stop on. You will need a winch to hold you on the hill if you have to stop!) We wont even open this trail is it has been wet!