Homer Fleming's Buck Marshall, Range Detective debuted in Detective Comics #1, in March of 1937. Buck would remain a regular feature up until issue #36. Detective Comics was the first comic book dedicated entirely to a single theme. In this case, detective stories. Each issue was 64 pages with various features. Most of them in color, but a few, like Buck were in black and white.
The story reprinted below hails from a later issue, #27. A comic book which is most often reprinted only because it marks the debut of another, more famous detective, Batman.
As you can see, Buck has moved on from being strictly black and white, to black, white and one color. Also, unlike his first appearance, Buck now has a pinto horse named "Pepper".
On a sidebar, I have a reprint of Buck's first appearance in Detective #1, but this just seemed like a better story to me. It is worth noting, however that in the previous story, Buck is also tipped off to the fact that someone has moved a murdered man's body by the presence of yellow clay.