  It has been noted anecdotally and through a small number of formal studies
that ambient lighting conditions and dynamic real-world backgrounds affect the
usability of optical see-through augmented reality (AR) displays; especially so
in outdoor environments. Our previous work examined these effects using painted
posters as representative real-world backgrounds. In this paper, we present a
study that employs an experimental testbed that allows AR graphics to be
overlaid onto real-world backgrounds as well as painted posters. Our results
indicate that color blending effects of physical materials as backgrounds are
nearly the same as their corresponding poster backgrounds, even though the
colors of each pair are only a metameric match. More importantly, our results
suggest that given the current capabilities of optical see-through head-mounted
displays (oHMDs), the implications are, at a minimum, a reduced color gamut
available to user interface (UI) designers. In worse cases, there are unknown
or unexpected color interactions that no UI or system designers can plan for;
significantly crippling the usability of the UI or altering the semantic
interpretation of graphical elements. Further, our results support the concept
of an adaptive AR system which can dynamically alter the color of UI elements
based on predicted background color interactions. These interactions can be
studied and predicted through methods such as those presented in this work.
