Do a bit of research....there are quite a few threads on this
Silver and gold are very close in birds....Silver is a gene which dilutes red in Chickens but not black. Gold is basically just the absence of silver. Silver is also a sex linked gene which means that males have 2 genes but females only ever have one and this is what enables the making of sexlinks.
Silver to gold and yes(if all else is the same) 50% of offspring will be hens same color as father and 50% of offspring will be impure males which are split half and half for silver and gold.
If you breed the impure male back to either silver or gold you will get 25%silver hens 25% gold hens 25%cocks that are same color as the mother and 25% Impure split cocks.
So as you see mixing silver and gold only makes three things ....silver, gold or cocks which look like impure dirty silver cocks.
As was said BLR needs the addition of Blue(to dilute black to blue) and also Mahogany(to make red instead of gold).
The only other color of sebright I know of is buff laced or white laced gold, which is possible because dominant white(which is a specific white gene) only dilutes black, making it white, but leaves red areas alone. Dominant white is also responsible for say Red pyle , where you add dominate white to an e+ partridge looking bird and it dilutes everthing except the red shoulders to a white color.