Do not use PWM if you are going to take photos.
(I'm no fan of PWM anyhow, as I can sometimes detect LEDs flashing at 5 kHz with the naked eye. The 100 Hz ones on the back of some cars are just plain stupid.)
If you have a PWM at 200 Hz, and you take a photo at 1/250th, then you will get a random 80% of the cycle. If you take a photo at 1/1000th, you will get a random 20% of the cycle, which is likely to be full on or full off. Mix that across several colours, all flashing with random phases, you can get absolutely any colour, and the photo certainly won't look like it appears in real life. Even at 1/60th of a second, you will get 3 and a bit cycles. The 3 cycles will average to what you want, but the remaining bit will be randomly somewhere between on and off, so you will get about a 10% variation on the brightness of each colour.
Go for adjustable currents. You do not get a great deal of heat dissipated, because the LED voltage does not change a lot. This is completely different from dimming incandescent lights, where the voltage changes a lot and the current changes less when they are dimmed.
If you use something like the "1A Voltage-controlled current sink" from this data sheet
https://www.linear.com/ad/19-current_control.pdf that will work very well.
If you have a 12 V supply, and three 150 mA LEDs in series, they might be 3.4 V at 150 mA and 3 V at 50 mA.
At 150 mA, the voltage drop in you current control device is 12 - (3*3.4) = 1.8 V so the power it has to handle is only 0.15 * 1.8 = 0.27 W
At 50 mA, the voltage drop is 12 - (3*3) = 3 V so the power is only 0.15 W.
If you use PWM, the maximum power is the same, because that occurs at 100% duty cycle so the current is on 150 mA all the time. The power dissipation at 33% duty cycle is 33% of 0.27 W which is 0.09 W, so less power is dissipated at light loads in the current control device, and more in the LEDs.