Font color applied in task instruction window (classic project) not correctly displayed in XTRF vendor portal.

If I apply color to a piece text using the editor in the task instruction window of a classic project, the editor applies a "span style" tag that doesn't seem to be recognized by browsers (or something else prevents the colored font from being properly displayed). I can see the color applied in the window, but the vendor does not see the colored font in the XTRF vendor portal.

If I go into source mode and change these tags to normal HTML font color tags, the text color is correctly displayed.

Why does this happen and how can I void it?

Thanks in advance.