As said, they do already look a little different. The KAR gear worn in the field was a low pillbox hat and shorts with British webbing or leather equipment, while the Germans had a high fez and trousers (KAR only tended to wear their fezzes for parade order once the war got going). They did tend to come to resemble each other more as the campaign wore on, though.
In most photos of them on campaign the KAR askaris don't seem to bother with the neckflap covers on their pillbox hats that figure manufacturers always give them, or they fold them back up against the hat, leaving the neck uncovered. I can only guess that they were uncomfortably hot, and they preferred the sun on their necks to having a cumbersome flap covering their head.
So some conversions along those lines could be in order if you want to distinguish them a little more on the tabletop.
Examples:



Note the mix of boots, sandals, bare feet, khaki and dark blue puttees, various smocks, equipment, different hats and three different types of rifle (one appears to have a Martini of some description while another has a state-of-the-art SMLE).

Later in the war some KAR units adopted large, shapeless brimmed sunhats. That's another option if you like doing conversions. There is even a photo of a KAR askari wearing a Wolseley sun helmet. With a few weeks in the bush, units on the British side looked every bit as ragtag as their German foes, but they did have the possibility of easier resupply, so it isn't a bad way to thematically distinguish them for tabletop purposes.