No apologies needed!
Yes, Red LEDs will be brighter though a red lens than a white LED, but only IF they started out with the same Lumens of light output.
The Red lens filters are not all that narrow in the passband so anything that looks red will be fine.
The reason I’ve not put LEDs in for the sidelights is simple. The replacements for filament bulbs do not have the cooling required to preserve the lifespan of the LED chips. Elevated temperatures vastly shorten their lifespan, and in those enclosed spaces they do get very hot.
Most LED manufacturers still specify the “half-brightness” lifespan with a mounting surface of 55C, and show degradation curves above this. Some typical figures from several firms (up until when I last looked two years ago) are 30,000 hours continuous at 55C, 150 hours continuous at 100C.
I fitted a Red LED in place of the NC rear fog light, knowing it will probably only be asked for a few tens of hours of use in the life of the car. Same reasoning for the reversing light. Both passed a recent MOT
When I fitted the DRL/Fog combination lights, I chose the Vinstar kit where a heat-sink is an essential part of the lamp design, and with both DRL and Fog lit in one on my test bench the back was only about 10C above room temperature after half an hour, and the LEDs inside about 15C above room, so I was very happy. They also passed the MOT, I know the DRLs are not required for this age of car, but the Fog did need to be correct aim of beam.
Most of my kitchen ceiling GX53 LEDs gradually lost brightness running at about 45C, and now after 11 years (about 33,000 hours) I’ve replaced more than half of them simply because of becoming dim. Still much better than filament bulbs however where 2000 hours to dead was typical. Those in the rest of the house with much less use have not needed changing. So I expect the LED DRLs I fitted to outlive my NC.