Hey,
As you might know the coal icon in this game has two different variants. One just the normal coal that you see on the belts and in the chests, and one with a yellowish background added.
Icons:
The Background is added so you can see the icons (whilst in "ALT-Mode") on chests, wagons, ... but on the Bots the icon without a background is used so they appear like black flying dots when transporting coal. This is the same for Logi aswell as Constr. bots.
Here a chest and a bot to comparison: http://imgur.com/73Mc8oA
[0.12.30] [kovarex] Wrong coal icon for bots in detailed mode
Re: [0.12.30] [kovarex] Wrong coal icon for bots in detailed mode
Thank you for the notice, it is fixed for 0.12.31 now.