I didn't want to make a new post as its pretty much the same topic!
If the red tailed shark is aggressive towards fish with similar colours, would it be agressive towards marbled angelfish? Who are black and silver?
What about guppies, sunset flame ones?
Penny.
The fish my shark is most agressive towards are the platys (various colors, from orange, black, red, grey etc) but it is hardly agressive to them at all now days, however, long ago before i adopted it it used to be in a tank about 20-30gals and was an aweful lot more agressive back then- having it in a densely planted and decorated 125gal tank has made it a lot less agressive.
I've never kept angels with RTS so cannot really say for them (although i think they probably wouldn't get along), but guppys should be ok.
In general though, it can be difficult to predict how agressive your RTS will be when it matures as it varies a fair bit from individual to individual- when small and young, they are hardly agressive at all, but when they grow to 4inches+ it starts to show a lot more as they mature.
Having a very decorated/planted tank which is not stocked to the brim but also has plenty of space to go around will help cut down on agression levels a lot- RTS feel most stressed when they have to share their space with fish that they feel threatened by or constantly occupy the RTS' space.
Shark-shaped fish should be avoided at all costs with RTS as RTS will certainly see these fish as threats.