I just dyed my hair lighter, and I'm going to Hawaii in a week. Will the salt water ruin my hair?
Professional Hair Care Answer - Nope, it sure won't.
Just be sure to wash and condition with products that are especially formulated for colored or permed hair. These products protect the hair shaft by adding moisture to it.
The salt in the ocean water may bleach it out a small amount, but I wouldn't worry about it if you're only going to be there for a week. Just have fun~
On the other hand, if you want to bleach your hair out some, salt water and sun over time will do it. If you mix the salt water at home instead of going to the ocean, mix it around 2 T. to a quart of water. Shake it well and let it dissolve before using it. You can spritz it in your hair each day you go out in the sun if you're not a the beach. It will only give you a gentle lift in color though. It will not damage your hair if you shampoo and condition as usual.
Lemons squeezed on the hair also works to lighten hair. If you have blonde hair, it will just get lighter. If you have darker hair, your hair will have red highlights, which always looks nice. To use lemons, squeeze the juice from 1/2 lemon in your hair and sit out in the sun for an hour, then shampoo and condition as usual.
The amount of lift you get varies. Brown hair will most likely turn red while lighter hair will turn more blonde.
Whatever you do though, don't use SUN IN if you are planning to EVER color or perm your hair. The only way to get rid of it is to cut your hair or grow it out completely, then cut it. SUN IN has metals in it. If you color or perm (perms especially) on top of these metals, the hair can MELT. I've seen it happen first hand in the salon. If your hair dresser asks you if you've used a product like SUN IN before, don't lie.
BTW - Dyed hair is simply called 'hair color' now. 'Hair dye' went out with the 60's.