* The "Red Gem": This is found on the Cinnabar Island Volcano. You need to use Strength to move some boulders and reach a hidden cave. The Red Gem is inside.
* The "Blue Gem": This is found in the Seafoam Islands. You'll need to use Surf to reach a hidden cave and use Strength to move a boulder to get the Blue Gem.
Here's a more detailed guide:
Red Gem:
1. Reach Cinnabar Island: You'll need to beat the Gym Leader Blaine in the gym on Cinnabar Island to gain access to the volcano area.
2. Use Surf: Surf to the right of the gym, past the rock and the island.
3. Strength Time: There will be a small cave opening. Use Strength to move the boulders blocking the entrance.
4. Get the Gem: The Red Gem will be in the middle of the cave.
Blue Gem:
1. Seafoam Islands: Travel to the Seafoam Islands, a maze-like area in the north.
2. Use Surf: Surf to the left side of the islands.
3. Hidden Cave: There's a hidden cave entrance on the left side of the island. Use Surf to reach it.
4. Strength again: Inside the cave, use Strength to move a boulder to get to the Blue Gem.
What to do with the Gems:
Once you have both gems, you can take them to Mr. Fuji in Lavender Town. He'll use them to create the "Rainbow Badge", which is a special item that gives you a slight stat boost.
Important Notes:
* The gems are NOT needed to complete the game or beat the Elite Four.
* This side quest is mainly for the Rainbow Badge and a bit of extra fun!