1 - Vapor4Life WOW Vanilla come in white. (KR808D-1) and there are blank white cartos at Vapor4Life and Bloogplanet. Re 510 - never seen any white prefills. However there are blank white Boge at nitelitevapor.us
Also - 510 has few decent prefills at all. It's a 3-piece acig and most cartos for it are blanks. KR808D-1 has lots of prefills because it's sold as a 2-piece.
BTW are you aware these models are a bit thicker than a cigarette? And white batteries make them look their largest. I find dark colors make them look slimmer. Like all decent slim ecigs, they are about 9.2mm diameter. And the short sizes are 180mah (about 1.8 hours of moderate vaping, with 220mah for the rubberized KR8 models or about 2.2 hours of moderate vaping though it will probably work out about the same since the ohms of the KR8 cartos are usually a bit lower.
2 - Yes there is a difference. 510 batteries are only 3.4v and KR808D-1 batteries are 3.7v (3.6v for the rubberized models Volt, Bloog, G6). Slim ecigs should only use standard resistance cartomizers/atomizers (about 2.5 to 3 ohm). The most popular standard resistance cartos for 510 are around 3ohm (barely warm on a 510 battery) and it is harder to find decent standard metal cartos in 510 threading closer to 2.5=2.6 ohm). The typical cartos for KR808D-1 are 2.5-2.6 ohm (Vapor4Life, Volt/Bloog/G6, KR808D-1 horizontal coils) for a greater difference between volts and ohms and a warmer vape, and a warmer vape gives more hit.
And BTW I recommend manuals for either. Harder to damage or kill with juice leaks, easier to get a good hit. And for 510 I recommend Joye only.
510 manuals are totally sealed on the threaded end and at least Joye brand 510 seems to have a long safety cutoff (long drag allowed) and I do only recommend Joye, Joyetech, Janty brand for 510. The rubberized KR8 model manuals seem totally sealed on the threaded end and have a bit more charge. But these models have a 5 second cutoff (max 5 second drag allowed which is a bit short for manuals since you want to press 1-2 seconds early to have vapor premade before starting your drag, leaving as little as 3 seconds for the drag. Vapor4Life has a custom 10-13 second cutoff where stated allowing longer drags than you will ever need, but the threaded end of the manuals still has a hole (though it looks blacked inside, we don't know how well)
I vape both (as manuals) and I put my juice that already has a rougher hit on the 510 and my juice that needs more hit on the KR8.
Ooo I am a veteran now! Makes me feel old haha.