Put some FILT that is coloured the correct colour so that it does not actually touch the source of heat you are using.

(That explanation was awful ik).

I used PROP for this and set FILT' colour manually. Just click on PROP and then choose "ctype". Now, you need to enter the special number (IDK How it works). For example: ctype:2446643 When you use this on FILT, its colour should be changed permanently.