Many today often equate the topaz stone as a light blue. In reality the blue is a rarity. Topaz comes in many colors including yellows, browns, pinks, purples, and more. Colorless topaz is considerably cheap and with radiation treatment will transform into the color we often associate the gem. It is probable the gem spoken of in Exodus was actually a clear as glass yellow.
Yellow Topaz and the stone Citrine (also yellow) are Novembers birthstones.
The Bible does not specify which stone represents which tribe. Among some scholars it is believed that Topaz represents the tribe of Isaachar.
*Although a Christian, I'm not a Bible scholar. I used the verses Ex. 28: 17-20 for the stone names and then modern stone recognition to design the block color.*
Sources:
Gemological Institute of America Incorporated. Accessed 2019 September. <gia.edu>
Bible Hub. Accessed 2019 September. <https://biblehub.com/commentaries/job/28-19.htm>
Franke, Mary. The True Meaning of November's Beautiful Birthstones. Brilliant Earth. Accessed 2019 September. <https://www.brilliantearth.com/news/the-true-meaning-of-novembers-beautiful-birthstones>