What do you mean on your screenshot i do see the pump being grey xd.
Ah you want it to be dynamic based on the class.. hmh ups then you will need to do add the classname infront of .ia_symbolComponent-pump-centrifugal...
like so .psc-NewStyle .ia_symbolComponent-pump-centrifugal{...} (psc- is auto added by igntion so is also needed)
Yes it could be located in a different file. i didnt check the files to make this, but used the google chrome debugger to look at the dom elements xd.
you should not manipulate the base theme.css files tho as these willbe overwritten again after an upgrade of igition. you have to make a new one so that doesnt happen.