If the green compound isn't too thickly applied*, and if it's held to the leather by some sort of oil/wax binder, it shouldn't permanently stain jeans much, if at all. I say this, because the belt I wear every day (with jeans) has green compound applied to a ~12" section of the inner (sueded) side. I used dry powdered compound (from a lapidary supply shop), and bound it to the leather with just some mineral oil-based hand lotion rubbed on after applying the compound, which really has done a good job keeping the 'green' on the leather, and not so much on my jeans' waistband. There was a little compound 'rub-off' to the denim early on, but regular laundering of the jeans has done a good job cleaning that up. As the belt/strop has been used more and the loosely-bound excess compound has been scrubbed off, it's really not an issue at all anymore. There's just a green 'tinge' left to the leather, and that's all that's needed for effective stropping.
* = The OP's picture might show it's a little heavy at the moment; some will likely rub off. Might scrub the leather with a dry paper towel, and remove most of the excess that isn't held tightly to the leather.
David