In order to ride the coloured gems you will have to get all the boxes and not die in the levels which give you a coloured gem instead of white

Yellow gem: The Lab
Green Gem: List city
Apricot: Slippery Climb
Blue: Toxic waste
Light orange: Generator room
Pink: Lights out

Once you have done this find the levels which have oloured gems in it (eg: jungle rollers) then ride the gems and you'll be able to get the white gem much easier.