Prickly pear does the colour and most of the body; lime and a clean blanco keep it from collapsing into syrup. The name is the colour: that short window when the desert goes magenta.
An ounce of prickly pear syrup and three quarters of agave is two sweeteners doing one job. If your syrup is already sweetened rather than a fresh tuna puree, drop the agave to half an ounce and taste before you pour.