We present a detailed experimental study of circle-marker detection algorithms based on color information. Three color spaces-HSV (hue, saturation, value), normalized color space rgb, and the gray-world normalization (NG) color space-are of main concern. We compare the algorithms based on these color spaces and combine them to use the color information simultaneously with shape-based marker detection techniques, and the Hough transformation, to achieve a new, robust, color-based circle-marker detection algorithm that gives higher accuracy. Experimental results show that the proposed algorithm is good enough to detect a circle marker in a complex background with various illuminations. (C) 2009 Society of Photo-Optical Instrumentation Engineers.