I just bought a male and female guppy, and the male guppy is really small, probably a month or two old. This is my first time getting a fish. The male guppy seems to have a black spot near his head. Can someone please tell me if it's healthy? The tail side has blue colour at some places only and it's greyish blackish near the head. Please help.
I assume you mean the weird color of the torso of the guppy.
It looks so weird because it's actually transparent and you can see the organs and the spine inside the body. Here's an example of 2 completely healthy guppies:
image source: Phys.org
The lower fish is completely transparent. You can see the spine and the silver and brown things in the stomach are the inner organs. Depending on the light, they can look silver, grey, brown or reflecting the color of the light.
The upper fish has partially pigmented skin. You can still see some features of the inside of the body, but you also see blue, yellow and black features that are only on the skin.
Here's another example:
image source: Wikipedia
The left fish is mostly transparent and the colorful spot you see on its stomach is the inner organs that can be seen through the skin.
In your picture it looks like the back half of the body and the fin are strongly pigmented, but the front half is partly or completely transparent. That's why it looks so different.