hex() converts a byte, char, int, or color to a String containing the equivalent hexadecimal notation. For example color(0, 102, 153, 255) will convert to the String "FF006699".
// Hex example size(500,220, P3D); background(20); stroke(128, 128, 128); fill(64); rect(1, 1, width-3, height-3); byte b1 = 23; byte b2 = 127; byte b3 = -127; byte b4 = -127; char c1 = 'A'; char c2 = '#'; char c3 = '9'; char c4 = 'Z'; int i1 = 255; int i2 = -65535; int i3 = 65536; int i4 = 429844428; color cl1 = color(255,0,0,0); color cl2 = #ffcc00; color cl3 = color(34,255,204,153); color cl4 = color(0,102,153,255); PFont font; font = loadFont("Arial"); textFont(font, 14); fill(32, 255, 0); text("Bytes", 5, 20); text("Chars", 5, 120); text("Ints", 195, 20); text("Colors", 195, 120); fill(255, 255, 255); text("b1: " + b1, 15, 40); text("hex: " + hex(b1), 80, 40); text("b2: " + b2, 15, 60); text("hex: " + hex(b2), 80, 60); text("b3: " + b3, 15, 80); text("hex: " + hex(b3), 80, 80); text("b4: " + b4, 15, 100); text("hex: " + hex(b4,2), 80, 100); text("c1: " + c1, 15, 140); text("hex: " + hex(c1), 80, 140); text("c2: " + c2, 15, 160); text("hex: " + hex(c2), 80, 160); text("c3: " + c3, 15, 180); text("hex: " + hex(c3), 80, 180); text("c4: " + c4, 15, 200); text("hex: " + hex(c4,4), 80, 200); text("i1: " + i1, 200, 40); text("hex: " + hex(i1), 370, 40); text("i2: " + i2, 200, 60); text("hex: " + hex(i2), 370, 60); text("i3: " + i3, 200, 80); text("hex: " + hex(i3), 370, 80); text("i4: " + i4, 200, 100); text("hex: " + hex(i4), 370, 100); text("cl1: " + cl1, 200, 140); text("hex: " + hex(cl1), 370, 140); text("cl2: " + cl2, 200, 160); text("hex: " + hex(cl2), 370, 160); text("cl3: " + cl3, 200, 180); text("hex: " + hex(cl3), 370, 180); text("cl4: " + cl4, 200, 200); text("hex: " + hex(cl4), 370, 200);