The DRLs can emit white light or, if the DRL function is provided by the same lamps that provide the front turn signal function, they can emit amber light. Separate amber DRLs that do not also provide the turn signal are not permitted.
Reverse lamps are photometrically incompatible with the DRL function, so that's a no-go. "Utility lights" are unregulated, all over the map and generally do not meet the requirements for a DRL.
Be careful if you decide to try to make your own DRL out of off-the-shelf lamps made for other functions (turn signal, etc.); most of them do not meet the minimum intensity requirements for the DRL function (500 candela on axis). The only LED units I'm aware of that meets the requirement is
this Signal-Stat unit, which comes in at 600 candela on axis. But here again, to be legal they'd also have to be wired up as the vehicle's turn signals, and since they were not designed for DRL service there might well be thermal issues with prolonged operation in the bright mode. I don't know of any dedicated DRLs in any of the US-standard truck/bus form factors (4" round, 2" x 6" oval, etc.).
There is a reason the (name brand/real) dedicated LED DRLs are expensive -- it takes a lot of engineering and top quality components to make one that works well and lasts an acceptably long time.