Hi all,my ka spat a load of coolant out the top of the expansion bottle the other day when i was sat in traffic for a while,temp light came on so i let it sit overnight at side of road and came back to it the next day.The coolant is now black as opposed to red before,obviously this doesnt sound too good

It does however drive perfectly and has plenty of go still and starts fine,is this definetly the head gasket gone or is there something else like an oil cooler that has failed? its a 2006 KA 1.3 petrol if it helps,thanks for any help