In this example Plot does not color each curve differently:

```
Plot[{vx0 Sin[t], vy0 Cos[t]} /. {vy0 -> 1, vx0 -> 1}, {t, 0, 12}]

```

but in this example it does:

```
Plot[{vx0 Sin[t] /. {vy0 -> 1, vx0 -> 1}, 
vy0 Cos[t] /. {vy0 -> 1, vx0 -> 1}}, {t, 0, 12}]

```

How do I automatically enable Mathematica to give a different color to each curve?