The harsh reality is that two-tone airsoft guns depreciate much worse than than their RIF equivalent when all else is equal since the market for two-tone is mostly those without a defence to buy a RIF.
60-70% of current retail (not what you paid) is your typical going rate for used RIFs in good cosmetic and functioning condition to nigh-on pristine and perfect functioning condition. Two-tone will often fall below 60% because you have a smaller market of people interested in buying them since most people with a valid defence to buy a RIF will buy a RIF over two-tone.
As EDcase said, to make the most money is to sell separately but it takes more effort and it will take longer to shift all of it. If you want it gone quickly, a bundle with a few deal sweeteners such as mags, ammo, batteries, a case, etc. will be your best option but expect to take a bigger loss than selling separately.
I know I'm twisting the knife in saying this but G&G's GC16 and CM16 series with ETUs/MOSFETs are among the worst airsoft guns to sell & resell because they're not price-competitive any more. You can get M4 derivative guns from Double Eagle and Specna Arms with integrated ETUs/MOSFETs that have more programmable features at a price that undercuts G&G's offerings massively.