MFColor mf;
mf.push_back(SFColor(1.0f,0.0f,0.0f));
mf.push_front(SFColor(0.0f,1.0f,0.0f));
mf[0].setRGB(0.0f,0.0f,1.0f);
but since it uses STL principles, you have all useful concepts such as iterator, algorithms, etc...
Below is included the documentation for this field type from the ISO standard.
5.3 SFColor and MFColor
The SFColor field or event specifies one RGB (red-green-blue) colour
triple. MFColor specifies zero or more RGB triples. Each colour is written
to the VRML file as an RGB triple of floating point numbers in ISO C floating
point format (see 2.[ISOC]) in the
range 0.0 to 1.0. For example:
fooColor [ 1.0 0. 0.0, 0 1 0, 0 0 1 ]
is an MFColor field, fooColor, containing the three primary colours
red, green, and blue.
The initial value of an SFColor eventOut is (0 0 0). The initial value
of an MFColor eventOut is [ ].