That's not the complaint against the Illinois flag; the complaint is that, even after being shown it, and being told what it is, you'd still have trouble picking it out from a row of state flags 24 hours later.

There are worse offenders than Illinois, though:

http://en.wikipedia.org/wiki/File:Flag_of_Idaho.svg

http://en.wikipedia.org/wiki/File:Flag_of_Kansas.svg

http://en.wikipedia.org/wiki/File:Flag_of_Kentucky.svg

http://en.wikipedia.org/wiki/File:Flag_of_Maine.svg

http://en.wikipedia.org/wiki/File:Flag_of_Minnesota.svg

http://en.wikipedia.org/wiki/File:Flag_of_Michigan.svg

http://en.wikipedia.org/wiki/File:Flag_of_Montana.svg

http://en.wikipedia.org/wiki/File:Flag_of_Nebraska.svg

http://en.wikipedia.org/wiki/File:Flag_of_New_Hampshire.svg

http://en.wikipedia.org/wiki/File:Flag_of_New_York.svg

http://en.wikipedia.org/wiki/File:Flag_of_South_Dakota.svg

http://en.wikipedia.org/wiki/File:Flag_of_Utah_(enhanced_var...

http://en.wikipedia.org/wiki/File:Flag_of_Vermont.svg

http://en.wikipedia.org/wiki/File:Flag_of_Virginia.svg

http://en.wikipedia.org/wiki/File:Flag_of_Wisconsin.svg

By contrast, once you learn one of these flags, you'll be able to identify it easily, even from a distance, and never mistake it for another one:

http://en.wikipedia.org/wiki/File:Flag_of_Maryland.svg

http://en.wikipedia.org/wiki/File:Flag_of_New_Mexico.svg

http://en.wikipedia.org/wiki/File:Flag_of_Quebec.svg