Some solutions
If a bulb failure system needs to be fooled into accepting the lower current consumption of an LED bulb, the normal solution is to connect a ballast resistor in parallel. This draws extra current from the supply and turns it into heat. Typically, a resistor that draws half the current of the original bulb will suffice. In the case of a 21W bulb on a 12v circuit, this means a 15ohm 15W resistor. A traditional indicator circuit may need to pass the full current, in which case try a 6.8ohm 15W resistor. The resistor does not need to be rated at 21W (as you would expect) because it is only on half of the time, and it's thermal capacity will average things out.

Use an active ballast resistor control circuit. This monitors the current flow in the LED bulb, and disconnects the ballast resistor in the event of failure. It makes the existing vehicle bulb failure circuit monitor the LED bulb as though it were a normal filament bulb.

Where there are several parallel circuits in an LED bulb, split them from the single current-limiting resistor and give them a resistor each. The new resistor value should be the original value multiplied by the number of series circuits.

Instead of buying commercial LED bulb units, make your own. This sounds a lot more radical than it really is - anyone with basic electronics knowledge and a little mechanical ingenuity can do it. Then you can design the unit using the most suitable colour and appropriate light level.