I use coloured leds in faded EM inserts, for example the GTB "Double Bonus" on last ball is often red and faded, so red led brings it up nicely, same for some of the yellow inserts where a warm white looks good and green inserts benefit too. You don't notice them as led but the colour is much stronger.
I do the same thing with colour matching coloured features in back glasses where the feature lits up - things like ball in play where there is a tight shroud around the globe so no light spill.
Flex leds under eject holes and star roll overs can make them a lot brighter too and not be noticeable if done judiciously.