⑮チャレンジしよう！の解答例

                
for i in 1...4 {
    color(0) //透明
    for j in 1...4 {
        drop(i)
        drop(i+6)
    }
    color(2) //緑
    drop(5)
    drop(6)
}
for i in 1...10 {
    drop(i)
    drop(i)
}
for i in 1...4 {
    color(0) //透明
    for j in 1...4 {
        drop(i)
        drop(i+6)
    }
    color(2) //緑
    drop(5)
    drop(6)
}