I would be interested in some before and after pictures.
Yes, and after one or two winters.
I suspect that red sand and red dye will make red. But yellow sand and red dye might make a lighter red, or even an orangy red.
You might need red and yellow dye though.
Ask the rep what colour you would get then if you mixed red and yellow dye
Remember that the maximum size of the sand particles should be roughly 1/3 of the joint size for the pointing to be effective, so you need to pick the correct sand.
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