Blue and purple are very close in the color spectrum. A CMYK blue set at 100% Cyan and 100% Magenta will look very blue on-screen and appear purple after offset print or digital print.
To resolve this issue, make sure Magenta is 30% less than Cyan when using very high Cyan values.
This will move the color further away from purple.
For best results Ask A Print Design Question before design time, or simply contact Minuteman Press Arlington at 817.472.7260.