Ok - send me the chip of paint and ill tell you how much of one colour to how much of another to mix together.
 The FINAL amount is done by eye - i could only guide you with this.
But if  i gave you the 2 colours either side of your colour ( pantone always works like this) then youd get a good idea of where you need to be with the mixing.


And yes - acrylics suck for matching and will take you ages to get right - enamels will not darken as they dry

Ok - the hole in the paper trick.

You have a small area of PF that you have touched up - you need to seal and protect this.
Gloss polyurathane works a treat - is hard wearing, comes in a spray can for $7 and is slightly yellowing - so adds to the authenticity of the restore.

Allow paint to dry and then a quick wipe over with meths to remove any grease etc. If the touch up area is about 20mm or so cut this size hole in a piece of paper.
 get your can of spray in one hand ready to fire. Hold the paper approx 60 -100mm above the pf directly over the restored area.
Now LIGHTLY spray the paper where the hole is in short squirts- do not concentrate on the hole in it, pretend its not there.
What happens is the spray goes through the hole and diffuses out blending perfectly to the rest of the pf.
Very light sprays are the go - maybe several of them.
it saves all the masking off etc and leaves no lines whatsoever where the polyurathane has met the PF.
 Guarantee that you will not see your new finish against the old.

REALLY simple and bloody effective!