This is the depth of good soil. Texas soils come in a wide range of colors. It is not fair to say one color is better than others, but there are some soils which have a better history of success. Deep well drained red sandy loan soils are the very best in Texas and possibly in the world. The red color is from iron oxidation which is a good sign of the presence of iron which is good and the presence of oxygen in the soil which is better.
Black soil is usually clay and also is usually very poorly drained.
However, do not rule out black soil because it can have a high calcium content and good soil structure. Brown soil is a combination of red and grey soils which can be good and is some cases very good.