I put my dehydrated kefir grains in one cup fresh whole milk and after 24 hours I change the milk and rainse the grains. But after three days they become molded. Befor this I put my kefir grains in near spoild milk and its color turned out with a bad smell so I threw them away.. What should I do now? Should I throw both the milk and the grains away?
The only safe thing to do is to throw it away. Preferably with a bottle or jar it is in, if you don't care for it. If you want to keep that jar, use dishwasher on it's hottest setting. I would also use sanitizers, but I have them readily available in my kitchen due to beer brewing. You can probably go without them.
Seriously, mold is really hard to get rid of, and it will get on other things in your fridge quite happily if you let it. Get rid of it as soon as possible.
To address what you didn't ask but probably should have, if spoil problems are common in your kitchen, it's time to clean it thoroughly, and then use some no-rinse sanitizers on it. Mold spores can stay in what appears a clean kitchen, too. And it never hurts to sanitize your fermentation jar and tools you use. Better safe than sorry! And it wouldn't be nice to have more failures.