The name “dark side” isn’t accurate really, both sides of the Moon recieve the same amount of sunlight. However, we can never see that side from Earth because the Moon is tidally locked. Basically, because of the way gravity works over very long periods of time, the Moon is spinning exactly fast enough such that one side always faces Earth. A lunar day is exactly one lunar cycle long. Seen from the Moon, Earth has phases which are 24 hours long, the difference bwtween them being literally night and day.
If you look around during the day, you can sometimes see the moon, but because moonlight is reflected sunlight it’s dim.
The side of the moon you see at day isn’t the dark side of the Moon, it’s the “bright” side.
The Moon is tidally locked with the Earth. It means that each times it does a full revolution around the Earth, it does a full revolution around itself. See it this way : turn around a tree somewhere. But carefully keep your eyes on the tree when you do it. You’re body turns on itself (aka, your foot are not always pointed toward the same direction), and you’ll find that you make a whole turn each time you complete a revolution around the tree. That is what the Moon does. No matter which part of the day, or night, no matter where you are on Earth, the Moon ALWAYS shows you its face. Not his back.
That’s why the other side is the “Dark Side”. Not because it’s dark (it ain’t, it’s the same colour), not because it’s in the dark (it ain’t, it receives light from the same the same way the “bright” side does), but because we can’t see it.
The reason you can see the dark side of the moon is [Earthshine](https://en.wikipedia.org/wiki/Planetshine). Sunlight hits the Earth, some of which gets reflected off, which hits the moon and then gets reflected back to the Earth.
And just in case it’s not obvious, the moon is not transparent during the day. The atmosphere is in front of the moon, so the blue light it scatters obscures anything less bright than it.
It is, but the sky is closer to you than the Moon so when the sky is blue there’s blue light coming from the direction of the Moon, which is more apparent when there isn’t strong light coming off the Moon itself.
Here I’m assuming you’re using “dark side of the Moon” to refer to the part of the Moon visible from Earth but not currently lit by the Sun, rather than the side of the Moon that’s not visible from Earth.