3. A method according to claim 2 , wherein: said at least one first colorable area is initially uncolored and forms part of a first set of initially uncolored, colorable areas positioned at locations between bars of said first barcode when said first barcode is in a first barcode readable state prior to exceedance of said at least one threshold, said at least a second colorable area is initially uncolored and forms part of a second set of initially uncolored, colorable areas positioned at locations of bars of said second barcode which appear only when said second barcode is in a second barcode readable state following exceedance of said at least one threshold, said at least a second barcode is in a second barcode unreadable state prior to exceedance of said at least one threshold, and as a result of said second set being uncolored, more than a single narrow barcode bar is missing from said at least a second barcode.
3. A method according to claim 2 , wherein: said at least one first colorable area is initially uncolored and forms part of a first set of initially uncolored, colorable areas positioned at locations between bars of said first barcode when said first barcode is in a first barcode readable state prior to exceedance of said at least one threshold, said at least a second colorable area is initially uncolored and forms part of a second set of initially uncolored, colorable areas positioned at locations of bars of said second barcode which appear only when said second barcode is in a second barcode readable state following exceedance of said at least one threshold, said at least a second barcode is in a second barcode unreadable state prior to exceedance of said at least one threshold, and as a result of said second set being uncolored, more than a single narrow barcode bar is missing from said at least a second barcode. 4. A method according to claim 3 , wherein said first set of colorable areas continues to be colored following exceedance of said at least one threshold.