OK - I'm going to wade in with my graphic knowledge ... - PLEASE NOTE ONLY WORKS IN THIS SPECIFIC SCENARIO
COLOUR WITH OVERLAYS TRANSPARENT WHITE OR BLACK AND ONLY AT 5% TRANSPARENCY INTERVALS
but that seems to be the question asked here ...
So after seeing these work around methods and not really finding them to be a satisfactory solution ... I use this method:
Select your base colour in CMYK values (lets say a nice green ... because green is a nice colour) ... add the shape in white over the top and set your transparency of the white shape (lets say at 50% ... because that's in the middle)
so we have our nice green base and our shape looking like a lighter shade of that nice green ... (lets call that ... nice pastel green)
to get CMYK values for our nice pastel green we first use our eyedropper tool ... and click on our background colour our base GREEN
now we have that colour selected ... go to the colour guide palette - and we see our base colour GREEN selected in the colour swatch go to the top right of the palette and the colour guide options and set the steps to either 10 or 20 ... (20 is max) that gives you tints of the colour from the base through to white or to black in 10% increments or in 5% increments (depending on if you made 10 or 20 steps)
I'm sure i'll get the haters because it won't work for two CMYK colours and blah blah blah ... but the OP asked for 60% on white and this is the quickest method that gives you the exact colour values
So I hope that helps in this case ... and if you want 37% transparency ... seriously choose 35 or 40 because any printing press in the world has 3% tolerance on its ink lay down on the dot so it actually makes no difference ...
and again any haters please don't give me the Heidelberg stats ... on dot screen and ink tolerance ... as your eye cant actually tell the difference either ...
its called practicality ... and real life experience ...
hope it helps ...
oh and colour has a U because i'm from England ... and I used green because that's my favourite colour and favourite has a U in it as well ... :)
Happy designing ...