MarbleDust sounds good to me, unless you can think of a better name
 
Just imagine Lightning Dust being protective over her little shy Marble, or getting all floofed up and pink cheeked whenever Marble would smile or chuckle at another one of Lightning’s Wonderbolt rants. Or maybe whenever Lightning would finish another Washouts show and got injured, Marble would come bounding towards her with a medical kit to bandage her up and treat her to a breakfast-in-bed morning the next day to help her recover. Imagine any other adorable scenarios with these two, and you’ll fall in love as I did
 
There’s a lot of Lightning Dust and Marble ships that I love (such as Lightning Dust x Trixie, Marble x Trixie, Marble x Twilight, Lightning Dust x Fluttershy, etc) but I’ve gotta say that currently this is my OTP, next to Twilight x Rainbow Dash and Zephyr Breeze x Thunderlane