Function print_field

    ∇ Z←A print_field Bg_Fg;Bg;Fg
[1]  ⍝
[2]  ⍝⍝ string A with given background/foreground colors Bg_Fg. If no foreground
[3]  ⍝⍝ color is given then compute it from the background color.
[4]  ⍝
[5]  Bg←1↑Bg_Fg ◊ Fg←¯1↑Bg_Fg ◊ →(1≠⍴,Bg_Fg)/1+↑⎕LC ◊ Fg←(Bg='WYORBGbw')/'bbbWWWwb'
[6]  Z←(⎕UCS 27),'[0'                      ⍝ normal mode
[7]  Z←Z,';3', Xterm_Color Fg    ⍝ foreground color
[8]  Z←Z,';4', Xterm_Color Bg    ⍝ background color
[9]  Z←Z,'m', A
    ∇