We discovered an issue today where LTI icons with a .nofilter class were still being affected by the filter. Please see this video for a description and explanation of the problem and how we fixed it with the following code. 

It seems like somebody overlooked the settings for no filter. 

#page .activity.modtype_lti .activityiconcontainer.courseicon img.nofilter,
#page .modchoosercontainer .modicon_lti.activityiconcontainer img.nofilter, 
#page #page-header .modicon_lti.activityiconcontainer img.nofilter