| Color Name | Pictorial sRGB Representation | Screen-Normalized sRGB Representation | Print-Normalized sRGB Representation |
|---|---|---|---|
| White | |||
| 202, 205, 190 #CACDBE | 251, 255, 237 #FBFFED | 255, 255, 255 #FFFFFF |
|
| Red1 | |||
| 157, 0, 29 #9D001D | 196, 0, 39 #C40027 | 199, 0, 43 #C7002B |
|
| Fluorescent Orange2 | Not calculated | Not calculated | |
| 255, 97, 0 #FF6100 |
|||
| Orange | |||
| 203, 83, 1 #CB5301 | 253, 105, 2 #FD6902 | 255, 104, 2 #FF6802 |
|
| Brown | |||
| 76, 39, 19 #4C2713 | 96, 51, 27 #60331B | 98, 51, 30 #62331E |
|
| Yellow1 | |||
| 205, 145, 0 #CD9100 | 255, 181, 0 #FFB500 | 255, 178, 0 #FFB200 |
|
| Fluorescent Yellow2 | Not calculated | Not calculated | |
| 255, 192, 0 #FFC000 |
|||
| Fluorescent Yellow-Green2 | Not calculated | ||
| 208, 235, 0 #D0EB00 | 229, 255, 0 #E5FF00 |
||
| Fluorescent Green2 | Not calculated | Not calculated | |
| 0, 153, 51 #009933 |
|||
| Green1 | |||
| 0, 75, 55 #004B37 | 0, 95, 71 #005F47 | 0, 95, 77 #005F4D |
|
| Blue1 | |||
| 0, 52, 90 #00345A | 0, 67, 114 #004372 | 0, 67, 123 #00437B |
|
| Light Blue | |||
| 90, 147, 193 #5A93C1 | 114, 184, 240 #72B8F0 | 144, 181, 255 #C7002B |
|
| Purple1 | |||
| 123, 0, 82 #7B0052 | 154, 0, 104 #9A0068 | 157, 0, 113 #9D0071 |
|
| Black3 | |||
| 27, 27, 27 #272727 | 51, 51, 51 #333333 | 0, 0, 0 #000000 |
Source: Federal Register – Vol. 67, No. 147 – Wednesday, July 31, 2002 – Rules and Regulations – Pages 49569–49575. Exerpt available online at http://mutcd.fhwa.dot.gov/texts/colorspecfr.pdf, accessed Saturday, March 29, 2008. Color coordinates were derived from arithmetic mean of the x,y coordinates of acceptable chromaticity box corners, and the geometric mean of the lower and upper reflectance limits for Types IV, VII, and VIII retroreflective sheeting. Future versions of this document may include nighttime colors as well.
The colors in the daytime Pictorial category are direct (except those marked with a 1) conversion from the FHWA figures. A perfectly diffuse, 100%-reflectance surface should theoretically be (255, 255, 255) white in this category; since practical materials do not have reflectances that high, most of the colors (other than the fluorescents) appear fairly dark. This category should be ideal for creating illustrations of road signs or other traffic control devices in context, where other objects in the scene may be brighter, or where fluorescent colors must appear to stand out. In advanced image editing software, the colors in this category are good for use with a "dodge" layer in front of them, containing a repeating gradient that goes from black to dark grey (or through a dark rainbow) to simulate the effects of microprismatic retroreflective materials. Since the D65 Standard Illuminant is the white point in sRGB, as well as the illuminant on which the FHWA daytime color specifications are based and the illuminant to which a human's eyes should be adapted in the daytime display of the road sign, no chromatic adaptation is necessary.
The colors in the Screen-Normalized category have been intensified from those in the Pictorial category, without changing color balance. These colors should work well for simulated images of road signs out of context, or for the color schemes of web-sites or other on-screen applications with road themes. (If the imperfect White is unsatisfactory, (253, 253, 253) should be considered.)
The colors in the Print-Normalized category have been normalized (by RGB scaling for simplicity – a better chromatic adaptation may be used in future versions of this document) so that White is (255, 255, 255) and should leave the print medium unchanged. Colors with RGB components greater than 255 after this step were adjusted by scaling each component uniformly, so as to preserve chromaticity. This category is intended for printing road sign imitations, with the relationship of the colors to White preserved, rather than absolute colorimetry. If absolute colorimetry is desired, and the output is to be viewed under D65 (daylight) illumination conditions, Screen-Normalized colors should be used instead, including that for White.
1These colors actually exist outside the gamut of the sRGB color space. The in-gamut color which best matches the FHWA specifications is listed here.
2Fluorescent colors exist outside the gamut of the sRGB color space. When in-gamut matches are used, the "fluorescent" colors only stand out when other colors are at a reduced value. Therefore, fluorescent colors are only shown here in the Pictorial category, except when there is no non-fluorescent color in that general hue, in which case the Print category is also shown.
3Black is not in the FHWA color specifications, because retroreflective materials are not made in black. Ideal black materials reflect no light; the blackest materials currently practical are about 2% reflective. Therefore, a 2% reflectance value was used to calculate Black in the Pictorial and Screen categories. The Print version of Black is "pure", which should result in a realistic, imperfect black level when printed. In future versions of this document, the other colors in the Print-Normalized category may be adjusted according to this effective blacklevel difference.
This document is copyright ©2008 Vid the Kid (me) and presents the results of calculations performed by myself and software I wrote in that year. My understanding of color spaces and the math involved was improved largely by articles on Wikipedia and the website of Bruce Lindbloom. Thanks.