Specifies the background color of the thumbnails when hovering the mouse over them (only affects unselected cells).
If set to clNone, then there is no change in color when hovering (so background will be ThumbnailsBackground).
Default: $00FFF3E5 (Explorer hover blue)
Note: ◼This value may be overridden by VCL theming colors. Set EnableTheming to false to prevent this ◼Not used if FillThumbnail= False or ietxFillWithImgBackground is defined in ThumbnailOptionsEx