First you want to know the code of the colour you have. Put the cursor in a coloured word and run this script in Applications > AppleScript > Script Editor.
tell application "Pages"
tell front document
set S to selection
tell body text
set C to color of character before S
display dialog (((item 1 of C) as text) & ", " & ((item 2 of C) as text) & ", " & ((item 3 of C) as text))
end tell
end tell
end tell
Then run the following AppleScript, after you have changed the example colours to the ones you found running the previous script:
tell application "Pages"
repeat with achar in characters of body text of front document
if color of achar = {53355, 23, 54} then
set color of achar to {23, 54, 53355}
end if
end repeat
end tell
