$1 and $3 are special perl variables. Inside double quotes
the '$' would need to be escaped (backslashed) if you want
them literally as is. I don't see the point of combining
perl and awk in this way, though.
I would choose one or the other for this.
Update:A perl solution is already given below,
so just for variety, here's an awk (maybe its nawk or gawk) solution:
#!/bin/awk -f
BEGIN {FS = ":"}
$3 > 1000 {print $1}