I suggest you go to the jewelry store you bought to clean it. Generally, a professional ultrasonic cleaning machine is used to clean jewelry with clear water, and the dirt on jewelry is cleaned through the vibration of water waves, so as to achieve the purpose of cleaning jewelry.
If you clean yourself, you can drop a small amount of neutral washing liquid into warm water, soak the jewelry, gently brush it with a soft brush, rinse it with clear water after a few minutes, and finally dry it with a clean soft cloth.
2) Maybe your diamond color is K or below. The color of diamonds can be simply divided into "transparent colorless", "nearly colorless" and "light yellow". Diamonds don't have Grade A. The English word for diamonds is "diamond" and the first letter is D, so international diamond appraisal agencies regard Grade D as the highest grade of color. The colors are D, E, F, also known as "transparent and colorless", giving people the feeling of clear as ice, which is hard to see in the market. The colors are G, H, I and J, also known as "nearly colorless", which is a good color and the first choice when buying diamonds. The color below K, also called "light yellow", can be seen by most people at a glance. With the increase of yellow, the value of diamonds plummeted.