well all of the above work - mostly painful i'll agree
deffo get a spectro for sure - and when you do look into katzper from nazdar - and read the instructions carefully unlike me i was doin it wrong to start with
or use the attached to help. open the file in text edit. change the Master C, M, Y and K values as you need. Now this is critical - 0 = 0 obviously. 1 = 100% ink ok! you want 35% tint of cyan then change the cyan value to 0.35
do NOT delete spaces or anything!
i've highlighted the areas in red (hopefully)
% ***** THE FOLLOWING FORMULA IS THE CENTER OF THE COLOR SPACE THAT WILL BE PRINTED *****
% ***** THIS EXAMPLE WILL PRINT C=0% M=0% Y=8% K=15%
/masterC
0.95 def % C in % for CMYK Master recipe *** MODIFY THIS ***
/masterM
0.70 def % M in % for CMYK Master recipe *** MODIFY THIS ***
/masterY
0.25 def % Y in % for CMYK Master recipe *** MODIFY THIS ***
/masterK
0.25 def % K in % for CMYK Master recipe *** MODIFY THIS ***
it's really important to not touch anything else. save as a new .ps file to your desktop. open that file in preview - preview will create a pdf. save that pdf somewhere then rip as normal and print. it generates a bunch of squares around your original colour
not brilliant but helps. your "colour" you entered in values is down the centre, and it puts the values of each swatch in - pick the nearest and try again.
but really - look into katzper from nazdar