Hi Bishwa,
The post shows only one composite image (the stack).
I could see some areas unusually dark even in the Blue, Green, and Red tiffiles. (Please see the images attached below) This is missing. Did you by chance forget to attach?
For the color variance (purplish color), you might want to have a look at https://community.pix4d.com/t/5396-Color-variance-problem-in-Orthophotos- and https://support.micasense.comhttps://support.pix4d.com/hc/en-us/articles/216541468-How-do-I-display-my-MicaSense-Multi-layer-GeoTiff-in-ArcMap-
Let us know if it helps.