Well, not wanting to be accused of sitting back and being a whiner, I looked at the effects.xml
The textures called up for the various effects (fuel leak and oil leak for example) looked to also be used in other effects so just making a "simple" graphic change is not the way to go.
However it would appear that how they actually look in-game is controlled by individual settings such as "Initial Color" and "Alpha" apparently at the beginning of the effect and then the ending color and Alpha for I will guess the end of the effect or end of the vapor trail?
The "0-255" color scheme and higher/lower on the Alpha can researched on Google I suppose but how a change looks actually in-game will be trial and error. And there are multiple lines for each effect (such as "oil leak") so there are different levels of oil leak graphics that can be called up?
Don't know but as time allows I may try to "darken" up the "Initial Color" and Alpha and see what happens.

Or if I am real lucky I have hit the graphics sweet spot and will have no more issue seeing them and I can just shut the hell up and enjoy myself flying my campaigns!