What compound would you recommend for the field?
So much depends on the steel and how you'll be using your knife. If you use the knife pretty hard, and more work is needed to restore your edge, a coarser compound may be better. On the other hand, if you reserve the knife for more fine-slicing tasks, the finer one may be enough to keep the edge in top shape. Depending on how you're going to sharpen the blade on stones, the size and tenacity of burrs left will also be a factor. Typically, green compound on a small surface-area strop won't be aggressive enough to clean up bigger and more stubborn burrs. That's where a more aggressive compound, like black (silicon carbide, specifically) or coarser aluminum oxide can be a plus.
You might take some time to use each of your compounds on other separate strops, to see which one will suit you best. Part of this depends on which compound leaves a coarser finish. If you first use the coarser compound on your new field strop, and decide later that the finer one would be better, you'll likely want to replace the leather with a clean piece. Embedded particles of coarser compound in the strop will effectively negate any benefit from the finer compound.
I'm betting your 'white' compound is coarser than the green (most aluminum oxide 'white' compounds are), but there's a huge range of variability in white compounds. Green is very small (typically) in particle size, and is usually used after a 'white' compound, for finishing. But some 'white' compounds will be of a softer abrasive (like tin oxide or talc, for example), and may not be as aggressive. That's why I suggest trying each on separate strops for a while, to see which one performs to a finer degree, and also to determine which will work best as a stand-alone field solution.
David