Vetwrap is a self-sticking bandage material available in a wide assortment of colors. It is often used to restrict movement of a pony's limb or to add support. It can also be used to restrain your pony. However, I think one of the best uses of vet wrap is covering a metal bit to prevent chipping of the teeth. It is not even necessary to completely wrap a metal bit, but rather only the parts of the bit that will sit on the teeth. Thus, you may not have to wrap over the joints if you want ot use a bit with a jointed mouthpiece (this is especially useful if you have mouthpiece with multiple joints).
Unlike polos, vetwrap is essentially good for one time use only (especially if you are using to wrap a metal bit), but I still really like it for restraint. Moreover, vet wrap is more effective as a restraint than polos because it is stretchy (you can tighten it more) and sticks to itself. One of my favorite uses is wrapping it over my rubber hoof gloves. This secures the hoof gloves to my lower arms making it really difficult to pull them off (actually nearly impossible if I'm also wearing a bit and cannot use my mouth), and it looks realistic because vet wrap is most often applied to the lower limbs (near the joint) of bio-equines for support. Also, vet wrap is available in many colors, including black, so there you can still achieve a "seamless" look.
If you don't have hoof gloves, you can also use vet wrap to force a pony's hands into fists. Simply have your pony hold his hand in a fist, then generously apply the vet wrap to secure them. Without the use of his mouth (e.g. if he's also wearing a bit or a face mask, muzzle, etc.), it is highly unlikely he will be able to free himself. Without the use of his fingers, you will not need to use locking tack on your ponyboy (a less bondagey look I know, but standard buckles look cleaner and are more appropriate for shows; also, from a pony's perspective, I find it incredibly frustrating to be so completely helpless even when my wrists are not restrained).
Color coordinating is easy: vetwrap is available in multiple colors. 3M brand vet wrap is available in 2", 3", and 4" widths, but you can find off brand "veterinary bandaging tape" in 6" widths as well. Regardless of brand, vet wrap is relatively inexpenive, which is good if you are using it to wrap a metal bit since you will want to change out the vet wrap after every use for sanitary reasons (it will become saturated with saliva fairly quickly). It's a great accessory which is easy to apply, easy to remove (by the trainer not the pony), and can match the color of your other tack. It can be used for restraint or decoration, and I always have a few rolls on hand.
Many fetish shops sell vet wrap (or non-name brand alternatives), but you should expect to pay 2 - 5 times more per roll than if you purchase it from a large online veterinary supply or horse tack house (the latter often charge a fee for orders under $50 USD, but it still may work out cheaper - or if you have bio-horses, then order stuff for them at the same time).
Thus, unless you are buying other bondage/fetish items at the same time and will save on shipping, you will likely be better off buying from a non-fetish retailer (you can get 4 inch wide 3M brand vet wrap for less than $2 USD even if you are buying a single roll). If you don't care about getting name brand vet wrap, you can find similar flexible bandage for even cheaper. I apologize if that last part came off as rant-ish, but it does annoy me when I see a 400% markup just because something is marketed towards adults (to be fair, a lot of prodcuts marketed as bio-horse items are also marked up, but this does not excuse the practice).
A couple places I have used in the past are (I usually get other equipment for my bio-horses at the same time though):