The WebGL extension WEBGL_color_buffer_float may be implemented (currently in draft status). Both OSX and iOS have the necessary underlying support available (either by way of ES3, or by way of color buffer float/color buffer half float).
Chrome started implementation of this ticket. Firefox now implements WEBGL_color_buffer_float unprefixed on OSX, Linux, Android and Firefox OS.
rdar://problem/19195632
Note that there's some controversy regarding this extension, see the public WebGL ML.
This extension was finally implemented in Bug 210994. *** This bug has been marked as a duplicate of bug 210994 ***