Nikon D5600 With sigma lens 17-50mm F2.8 lacks color depth?

I have Nikon D5600 With sigma lens 17-50mm F2.8 lacks color depth. Means the sky does not look clear blue and such as other things also like grass. Also there's lack of exposure in every picture even when the camera meter balance for exposure is little high. Why i face these problems?

Exposure meter is high to the plus side? That means the pictures are overexposed. If you don't get it yet, there's too much light washing out the colors in your pictures which caused exactly what you are describing - lacks color depth.

Why you face these problems? I won't go into that. Instead, I'll just recommend you learn photography.

Check whether you have the camera set to an inadvisable "Scene" setting. And look at the instruction book. There are several reasons why your pics might seem a bit colourless, indeed exposure level (as noted by Keerok) is one of them.

You're taking photos of landscapes with the lens at its widest aperture? The minimum lens aperture when taking photos of near to far photos would be F8. The wide aperture allows you to a picture where only what is focussed upon is in focus. A portrait at 50mm and F2.8 will give a knee to head shot of the subject, so you close distance until only the face is in focus then take your shot but only the face will be in focus, the near background will be blurred out.