Substitute a color in an EPS

Hi,

I must edit an EPS to change the color of the shapes. Since it's an
EPS, I cannot edit each shape separately (moreover, it's a vectorized
image from an old logo). If I select all the objects and change their
color, it won't work well: the logo consists mainly in a circle
embedded in a square; the circle is transparent, so what you actually
see are the corners of the square as four triangles with round
hypotenuses. If I select the whole thing and change its color,
everything changes color, including the internal, transparent circle,
so all you see is a square.

So, how can I change the color of only the triangles?

Thanks in advance.

Raph