A ▁calls ▁for ▁a ▁mon och rome ▁frame ▁and ▁icon ▁( us ually ▁black ▁or ▁in ▁accord ance ▁with ▁the ▁affili ation ▁colour ). ▁NAT O ▁symbols ▁can ▁also ▁be ▁rendered ▁with ▁fill ▁off ▁using ▁a ▁frame ▁col oured ▁according ▁to ▁affili ation ▁and ▁a ▁black ▁icon , ▁though ▁this ▁is ▁not ▁defined ▁in ▁any ▁AP P - 6 ▁standard . ▁ ▁Aff ili ation ▁Aff ili ation ▁refers ▁to ▁the ▁relationship ▁of ▁the ▁tra cker ▁to ▁the ▁oper ational ▁object ▁being ▁represented . ▁The ▁basic ▁affili ation ▁categories ▁are ▁unknown , ▁friend , ▁neutral , ▁and ▁host ile . ▁In ▁the ▁ground ▁unit ▁domain , ▁a ▁yellow ▁qu at ref o il ▁frame ▁is ▁used ▁to ▁denote ▁unknown ▁affili ation , ▁a ▁blue ▁rectangle ▁frame ▁to ▁denote ▁friendly ▁affili ation , ▁a ▁green ▁square ▁frame ▁to ▁denote ▁neutral ▁affili ation , ▁and ▁a ▁red ▁diam ond ▁frame ▁to ▁denote ▁host ile ▁affili ation . ▁In ▁the ▁other ▁domains ▁( air ▁and ▁space , ▁sea ▁surface ▁and ▁sub sur face , ▁etc .), ▁the ▁same ▁color ▁scheme ▁is ▁used . ▁ ▁The ▁full ▁set ▁of ▁affili ations ▁is : ▁ ▁P ending ▁( P ) ▁ ▁Un known ▁( U ) ▁ ▁Ass umed ▁friend ▁( A ) ▁ ▁Friend ▁( F ) ▁ ▁Ne ut ral ▁( N ) ▁ ▁Sus pect ▁( S ) ▁( ass umed ▁host ile ) ▁ ▁Host ile ▁( H ) ▁ ▁Ex erc ise ▁pending ▁( G ) ▁ ▁Ex erc ise ▁unknown ▁( W