https://powdertoy.co.uk/Wiki/W/Elements:Tools.html#Sign

Blue sign is the link to another save. Usage: {c:SaveID|Click here!}

Yellow sign creates spark when someone pressing it. Usage: {b|Click me!}

i dunno how too

purple???

Although this thead is a bit old now, but still if someone needs help with signs, here's a tutorial save about sign tool that i made recently,

Actually, the link signs aren't blue, their color is cyan, a color where green and blue mixes.