CSS 1, Section 5.5.16, border-color property says: "If no color value [for the border] is specified, [then] the value of the 'color' property of the element itself will take its place."

CSS 2.1, Section 8.5.2, border-color property says: "If an element's border color is not specified with a border property, [then] user agents must use the value of the element's 'color' property as the computed value for the border color."

CSS 2.1, section 8.5.4, border property says: "Since, to some extent, the properties have overlapping functionality, the order in which the rules are specified is important."

Firefox 2.0.0.6, Safari 3.0.3, Opera 9.50, Konqueror 3.5, Amaya 9.55, Seamonkey 1.x, Seamonkey 2.x, NS 6.2, NS 7.0, NS 7.2, K-meleon 1.x, Galeon 2, Epiphany 2 all pass this test.