Turn off paint

You actually don't need to turn off the paint to see the miters. Miter display is controlled with the icon circled below in the Display dialog box.

Be aware that if you use fillets on a joint, then the miter will not display.

Although it's not required, turning off the paint will make miters stand out more. You can turn off the paint by selecting from one of the other display modes described at: bikecad.ca/display_modes.

Could you please send me a copy of your BCAD model?

It turns out the confusion here was caused by the fillet feature. I had explained that if you want the contour of the miter to appear, you must turn off the fillets at that joint. In the case above, the fillet size was set to zero which theoretically should mean you don't have a fillet there. However, the image next to the fillet size input fields is actually a toggle button. You must toggle the fillet off, not just set the size to zero.