Slab are darker than actual normal block

As a builder, I like to decorate my houses in Minecraft and for decoration I use quite a lot of slabs and stairs and they make the house look extraordinary but I think I found a bug with slabs and that is, if you compare the slab to a normal block side-by-side you will see that the slab is actually darker than the normal block. For Example :- Put a Smooth Quartz Block and then on the side put a smooth quartz slab you will definitely see the difference between the darkness and brightness of them and also it's not just the Smooth Quartz Block and Smooth Quartz Slab that's have this issue but also the other blocks and slabs.