Both are beautifully executed, and I love & admire them.
The 5231 has brighter colors (vibrancy to me is important for enamel dials) vs 5131, whereas 5131 has more colors and to my eyes better color gradations.

Based on the color gradations exhibited, I believe that the 5231G was likely made by the team that produced the 5131R in which different colors are more distinct, whereas 5131G was created by Anita Porchet and team with a different gradation technique.

When I get a chance to examine a 5231G in the metal, I will write a deeper review for the comparison.