No pictures but it is almost true. This one is based on science, not just something you read on the internet. Read the very first post in this thread for the science.
Tadkerson’s Sex Link Thread
https://www.backyardchickens.com/forum/viewtopic.php?id=261208
The reason it is almost true is that the black is wrong. A RIR rooster over a Light Brahma hen will produce a Red Sex Link. Males will show yellow and females will show red. Black has nothing to do with a Red Sex Link as far as determining sex. That red can be different shades of red too. Some crosses will give you a dark brown but some give you a fairly light reddish color, sort of a buff. It could be many different shades of red. Instead of saying dark brown/black in your statement, say reddish.
Some sex link crosses will produce solid yellow or red chicks but some will produce chicks that are only yellow or red in certain spots. It helps to have those chicks side by side to compare them. I have not done your specific cross but I’d expect the chicks from that cross to be pretty solid red or yellow and real easy to tell apart.
You can try browsing through that thread I gave you above for pictures of red sex link chicks. It’s a real long thread and I don’t know if anyone has photos of your specific cross or not. But if the rooster is a pure RIR and the hen is a pure Light Brahma, you have red sex link chicks.
