Blue semi transparent stain for new deck on treehouse

Hello. I am new to this site. I live in new jersey. Very humid summers. I am building a treehouse for my son, and was interested in finding a semi transparent stain for doug fir that i am using for my decking. I know this is not the best wood to use, but it was very nice looking wood, and was pretty clear. My som wants a dark blue stain, and so i was going to get the behr semi transparent premium deck stain, until i saw your reviews. I also noticed that you do not recommend staining it right away, so i will wait. The two brands you recommend for use on new wood did not come in any funky colors. Thanks in advance for your advice!
Chris