2.1.9 [W3C-CSS3-Color] Section 4.4, 'currentColor' color keyword
The specification states:
currentColor The value of the 'color' property. The computed value of the 'currentColor' keyword is the computed value of the 'color' property. If the 'currentColor' keyword is set on the 'color' property itself, it is treated as 'color:inherit' at parse time.
Quirks Mode, IE7 Mode, and IE8 Mode (All Versions)
The currentColor keyword is not supported.