Theories that the Daenerys will die in Season 8's Great War abound, and her hair change could reinforce this unfortunate theory. First of all, Season 7 saw Dany give a speech eerily similar to the one Khal Drogo gave before he died, and fans have been closely watching the Mother of Dragons, suspecting that she might end up going mad like her father, Aerys II Targaryen. Could it be Dany's birthright to get power hungry and violent, just like her father did?
During Season 7, GoT fans watched Dany reject Tyrion and Jon's advice to be different from past rulers (like her father) by sticking to peaceful solutions, which resulted in Drogon getting hurt and Daenerys almost being killed. While Clarke's bold new hair color could remain under the iconic Mother of Dragons wig, fans will likely become wary if Dany's sporting an Aerys-like hairdo in the upcoming season.
The fact that Season 7 also reveals one of Dany's dragons, Viserion, became a wight suggests that she might not be as powerful as Daenerys stans might hope. In a vision she had at the House of the Undying, she saw that her fate might not include the Iron Throne. Though she reaches out to touch it, she then seems to realize that her pursuit of it only leads to death and destruction. Perhaps Season 8 will reinforce this theory as well.
It's always a guessing game with Game of Thrones, and, though nobody can be too sure what Clarke's decision to dye her hair platinum blonde means for Daenerys Targaryen, it's almost certain that a lot will happen for her character in Season 8 — tragically or otherwise.