What is the default background color of custom entity icons in MSCRM ?

Hi,

I have created five custom entities without applying any background color to the icons in solution supporting CRM 2016 and dynamics 365. 

But among them, 3 entities are showing green background color and 2 are showing grey background color.

Please help me to understand how MSCRM is considering the default colors of the entity icons. I want them to display having same background color without explicitly doing any customization.  

https://www.screencast.com/t/vxhIczsf

Please suggest.