PLA flexure performance isn't black and white

I made two black PLA driver stages and they worked fine. I made a white one and it didn't. Hmm, time for science. I made two 100mm beams with a flexure and anchor on one end, and put 20g (OK, two 158 grain .357 lead projectiles, which is close) on the end of each.

Camera lens positioning is tricky here, but the anchors are 38mm above the desk. The black PLA drops to 22mm, and the white PLA only drops to 28mm. My maths is generally suspect, but this indicates to me that the white PLA is significantly stiffer (10mm deflection vs 16mm deflection) and that this is affecting the performance of the flexures in the stage.

For reference, the PLA is the stuff I used to make as Diamond Age using Ingeo 3251D PLA (a relatively low molecular weight). The white is '3DEA Paper White' and I have no idea what they use but I suspect (a) most manufacturers are using higher molecular weights these days, and (b) it is packed with a lot of whitener which will affect the stiffness anyway.

So from here, I make another in black and see if it works, then produce modified flexure designs to match the flexibility with the white and test a stage using those flexures. [Edit: A third black PLA drive stage works fine.]

It may be that I need to include a stiffness test article for people to use to optimise their μRepRaps.