Right now midjourney fails rather badly at this. Examples below.

The claim is: before EOY 2023, I can run this prompt "a red triangle on a blue cube" and get success in midjourney at least 15/20 times. Right now it appears to be quite random. I will run the prompt 5x to produce 4 images and use my judgment to evaluate.

If it appears mj is specifically tuned to this, I will vary the colors/shapes/order to verify if it's a real capability or not, although that is very unlikely to be necessary.

Here is a new competitor, Ideogram's version of the image:

These all make sense - the triangle hasn't morphed into a triangular pyramid. And it's on a cube, and the cube is visible. Arguably 4/4 success.

Color flip version: also great.

Midjourney V5.2 version from 8/28/2023 - note that it's ignoring color swapping. In addition to completely ignoring color swap, these also all fail to show a cube.

All of these would fail for me.