So there is several ways to get a little color in your hair, you can choose to spend hours getting it done, or you can go to a Holi party and have it totally destroyed in seconds looking like a Unicorn on ice!
It’s ok it’s a natural color and washes out, it will do no harm? Seriously that is so far fetched it’s not funny, it stains and on blonde hair will be almost impossible to get it out, it stains better than any color be it paint or lipstick once it’s there good luck getting it out!!
Can you put anything on it to prevent it from staining your perfect blonde…. easiest answer is NO, you can soak it in oil, mask, a styling paste, gel etc etc but I assure you it will still find a way to get through and ruin your hair. You can wear a scarf but when water is added and coloured powder meet then it will go through all material so the easiest suggestion is avoid the random throwing of coloured powder if you love your color, if you don’t mind looking like a unicorn 🦄 for a while then go for it!
Best to get a pre Holi treatment like Alfa Parf linseed treatment which will close the cuticle tightly which will help reduce color absorbing.