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.
Note that there's some controversy regarding this extension, see the public WebGL ML.