**Riddle Answer: The Egret**

The answer to the riddle is the Egret, a beautiful bird found in various parts of the world. Let's break down the clues given in the riddle to understand why the Egret is the correct answer.

**1. "I am white in color, not milk":**
The Egret is known for its distinctive white plumage. Unlike milk, which has a creamy white color, the Egret's color is a pure, bright white.

**2. "I catch fish, not fisher's net":**
Egrets are skilled hunters and primarily feed on fish. They have a long, slender beak that they use to catch fish from lakes, rivers, and other bodies of water. This clue suggests that the Egret catches fish in a natural way, rather than relying on a fisherman's net.

**3. "I do dhyanam, not a sanyasi":**
The term "dhyanam" refers to meditation or contemplation. While a sanyasi is a Hindu ascetic who renounces worldly possessions and pursuits, the clue implies that the Egret engages in a form of focused concentration similar to meditation, but without being a sanyasi. This is likely a reference to the stillness and patience with which the Egret waits for its prey, displaying a sense of calm and concentration.

**Conclusion:**
Based on the given clues, the Egret is the most fitting answer. It matches the description of being white in color, catching fish naturally (not through a net), and displaying a sense of concentration similar to meditation. The Egret's hunting behavior, distinct white plumage, and serene presence make it a perfect match for the riddle.