I have 661 and have the issue. When off I can read them when on I can not. White backing and bolder font would help but I doubt CG would even warrant an expensive fix for a minor issue like this.
Personally I believe a fix would be a dimmer LED or a different color LED. Maybe. Need to test this. The white is so bright that does no help. The original incandescent were 1/2 the brightness. Like trying to see someone standing in headlights its hard to see.
Also the faceted prism like insert does not help as it magnifies the simmer of the led, etc.
Maybe CG can mess with software brightness or color variants in the software to fix this.
Would I like a new insert PF with super black lettering? YES! But I am ok with this since its a very expensive fix for CG (if they have to replace) and its not really a big deal. We know which King were shooting.