You can get what you want, but every shop is independent and some have better equipment than others, along with different color choices.
I would caution one thing: if you are serious about a solid white base, MAKE SURE you see in person an example of a showerbase already installed in a customer's home at least six months old. It is mandatory by fed regulations to have a non-skid surface film applied to all bottom surfaces - and a good thing that is, too; because there's nothing slippier than these glossy non-porous flat surfaces!
Some of these films really 'catch' dirt and are hard to clean. You need to be very sure your vendor has used a non-skid surface where you won't have this maintenance issue.
Our showerpan is tan cultured granite-look and we absolutely love it. We would do it again in a heartbeat. It's 9 yrs old and in perfect shape, also ridiculously easy to keep that way!
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Glass doors
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