Right clicking each cube and then navigating their menu system would be....... more painful than I would like to think about
If they need inspiration on a good-extremely-fast and user friendly "Tool" which changes the surface style of a block... Empyrion has a good one. However due to how DU uses "RMB", pulling up the tool's color/texture chooser may end up another convoluted mess of hand stretching around the keyboard to some obscure key, or combo of keys.
For those not acquainted, it would be a tool that lets you choose a color and/or texture, then anything you aim and click on, changes to it (if the material can, given some materials lack certain colors/texture styles). Basically allowing you to 'spray paint' blocks with a continuous mouse-down & move-around action.
It really is simple to use. Far easier than figuring out which block to construct in a mile lone listing of blocks, wrestle with it in your inventory and to a sidebar slot, and fiddling with different tools, and swapping or placing the block down ...... only to find out "nope, that color/style doesnt look good here" .... and starting all over again.