Screen flickers on IGEL Thin Client while using XenApp 6.x (EnableOSS)

When you experience flickering of certain (in our case on blueish) parts of an internet website which being connected to a XenApp 6.x farm using a IGEL Thin Client you might need to read these Citrix articles :

CTX133935 - Flickering or Other Display Issues Might be Seen when Adaptive Display or Progressive Display is Enabled and CTX128332 - Images are Tinted Blue in Published Photoshop

This can easily be eliminated by setting the following setting in the setup of the Linux thin client:

IGEL Setup -> System -> Registry -> ICA -> wfclient -> enableoss -> ◘ Enable off-screen drawing.

Unthicking this setting eliminates the problematic progressive / adaptive display feature when using OSS (Off-Screen Surfaces).