Play with it (in small amounts) & see what you like ... especially once it's underwater & under your lights (which can significantly change the hue of pale sand).
My personal preference is to have one sand dominate & the other accent, rather than a 50:50 mix
The light sand will add strong contrast & brightness to the substrate (no idea how much you intend to plant over) ... if you have fish in mind for this tank, also consider which sand will best set off the fish (generally fish feel more comfortable with darker/dimmer substrates but I think with the amount of rock, you can choose whichever you prefer & fish will be fine)
It's a great rock scape!
My personal preference is to have one sand dominate & the other accent, rather than a 50:50 mix
The light sand will add strong contrast & brightness to the substrate (no idea how much you intend to plant over) ... if you have fish in mind for this tank, also consider which sand will best set off the fish (generally fish feel more comfortable with darker/dimmer substrates but I think with the amount of rock, you can choose whichever you prefer & fish will be fine)
It's a great rock scape!