Pictured above is a pair of ALL WHITE Handup gloves dirtied by about 2 months of riding (Twice a week to be exact.. we aren't trying to be race ready or anything). The reason we said "the above pair" is because, the two images are ACTUALLY the exact same gloves.
The image on the right is the same pair of gloves, after it's day at the Spa A La Kitchen Sink. After a small lather of washing detergent (we recommend Tide due to their incredible 2018 Super Bowl Commercials and nothing more), these gloves took a 5 minute soak-n-scrub in warm sink water. They were then left to tan in the sun! They can be left anywhere to dry but the sun provides all that Vitamin D for an A+ glow-up.
In sincerity, warm water, a scrub, and allowance to air dry is all our gloves need to get a nice clean! And quite frankly this is what your gloves look like regardless of whether they are all white or not. It's good to do this regularly to remove dirt from the palm (gross..) degrading sweat from the seams (very gross), and Snot from the terry cloth thumb (Ultimate GROSS!!!).
OR, you can simply toss it in the wash with your other riding gear and allow them to air dry. This what we call the "Easier method."