This indeed applies to dimming of all colors that are not equally mixed (same color value for each of R,G & B-combination). It took me a long time to realise, that a real helper is the use of setting the led color with HSV, where Hue sets the color, Saturation makes the color more white-ish and finally Value, which changes the brightness of the chosen color while keeping the mixing ratio of the RGB-colors..
The only challenge is to find the correct HUE- and SAT-values to get the warm-white you would like to have.
helpful links:
Adafruit library guide - HSV-colors
RGB to HSV conversion