Gazebo has its markers, too. And... though I can not believe it myself...
looks like... you can not change colors for them!
Also, it is not very elegant in the first place:
This was a single marker, sticking out of the ground... I am not going to use this approach anyway.
Using objects instead of markers is kind of an obvious solution
(to "can not change color" problem). Just an important moment
An object should have "static" property, so that physics engine doesn't spend time on it.
Here is an example:
And here is the URDF for this "marker" (I just took an existing URDF, I am not going to use this approach as it is ugly):