Upload & Sell: Off
I think your pictures generally look okay, Dave - shot in harsh light in some cases and a tad overexposed occasionally. The biggest problem that I'd foresee—unrelated to anything being discussed here—is that you seem to submit a lot of 'similars', which are likely to significantly harm your ranking.
The colour problem is something of a red herring with Alamy. As Scott is pointing out, their previews are likely to appear inconsistently because they're untagged, so then the combination of monitor gamut and browser behaviour comes into play with endless permutations possible. Alamy have pretty much dispensed with colour management, probably because with over 30,000,000 images the saving in storage and bandwidth is significant? Anyway, the net result is a total disregard for colour fidelity all the way to the customer—it's left to their interpretation.
Better to buy a high-end NEC because you like nice things rather than believe it'll help you on the stock photography front, particularly with the cavalier stock supermarkets!