More protective case colors were originally suggested, but (now this is my speculation) I think it is unlikely now that a transparent one will be produced. The reason is that the rationale behind a transparent case is/was that it would allow some peek into the phone’s internals. With the launch of the FP3+, I believe that the FP3 will be discontinued sooner or later when remaining stock has sold out. At that point, all remaining Fairphones will be completely opaque and a transparent case would lose its most important “selling point”. You might have already read that the decision to go all opaque is an ecological one – the translucent FP3 could only use 9 % recycled plastics, the opaque FP3+ 40 %. I cannot imagine that Fairphone would go back on that improvement in terms of sustainability.
When it comes to the bumper, allowing a peek inside the phone was also a selling point (you already described this). While I doubt that Fairphone will keep producing bumpers (or even offer them as a standalone accessory), I think there is at least a slightly better argument to make for offering it – it could be justified as a more affordable protection option (compared to the protective case), although I am not sure that its actual production costs are dramatically different.