add a sample of overriding the background color to the demo
add a sample of overriding the background color to the demo

harlanhaskins/FSImageViewer,iwakevin/FSImageViewer,freshbrix/FSImageViewer,sirajudheen53/FSImageViewer,shenhzou654321/FSImageViewer,Voxer/FSImageViewer,imjerrybao/FSImageViewer,x2on/FSImageViewer,yichizhang/FSImageViewer,arsalananwar/FSImageViewer,tooploox/FSImageViewer,ListFranz/FSImageViewer