color palette: use dijit tooltip for color information

[becky]

currently the tooltip uses the title attribute to provide the color information via a browser generated tooltip. This is useful for situations when loading of images is turned off so the user can figure out which color to pick. But, since the title attribute doesn't work for keyboard users, a keyboard user with images turned off has no idea what the color is. We have added alt text to the color palette image but it really isn't usable.

So, it would be nice to use a dojo tooltip which will display on focus. But, this could be annoying for users as they arrow thru the color pallete (and particularly so for screen reader users so I'm wondering if it would be possible to do this only when a11y mode is detected?

[bill]

This is also recommended from IBM Design Leadership recommendations, I guess for consistency in LnF.

[doughays]

see also #3876