If you right-click your layer and go to:
Properties > Labels
Use the Show labels for this layer
option, select the field to label with and then click the data-defined button for the Color section as shown below:

Then enter an expression like:
CASE
WHEN "Field" = 10 THEN color_rgb(0, 0, 255)
WHEN "Field" = 15 THEN color_rgb(0, 255, 0)
WHEN "Field" = 25 THEN color_rgb(255, 0, 0)
ELSE color_rgb(0, 0, 0)
END
or
CASE
WHEN "Field" = 10 THEN '#0000ff'
WHEN "Field" = 15 THEN '#00ff00'
WHEN "Field" = 25 THEN '#ff0000'
ELSE '#000000'
END
Click Apply then OK and hopefully you should see your labels with different colours:

Tested on QGIS 2.16.1-Nødebo.