Photography

Hello photographers! I am a private horse trainer and part of what I have been training the horses to do is specific things for photo shoots such as training them to look a certain direction on command. We expect to have people who know NOTHING about horses or how to control them to book photoshoots so I’m trying to dummy proof everything so I can control the horse from out of shot. Things have been going well but one of the things I will be training next is to use an object as a marker and train the horse to go to where it is on command. This will make things easier however whatever object I use will be in the shot and need to be edited out afterwards. What object and color would be easy to edit out? Some examples of what people generally use are cones, cut and colored cardboard, a square of carpet, a piece of interlocking foam flooring, etc. I would need to use a color other than green and brown/tan as the horse may not be able to see the marker if the ground is the same color. Suggestions appreciated!