What is the best substrate for marbled gecko

[bucket]

I'm trying to find out what would be the best to use for my w.a marbled geckos. Should i use washed sand, red sand or something like coco?
Any ideas would be great.
What do you guys use

 

[Bluetongue1]

Sand is fine. Colour does not matter. They are found primarily on yellow and white sands and to a lesser degree red soils. They are primarily arboreal or rock welling. They are nappy on most substrates so long as they have plenty of furnishings to climb on. I hope this reply isn't too late

Blue