Changing the plot variable inside Plot [duplicate]

Possible Duplicate:
Difference in Plot when using Evaluate vs when not using Evaluate

Assume one has vector of functions (e.g., vec={x,x^2}).

The command Plot[vec, {x, -2, 2}, PlotStyle -> {Blue, Red}] allows one to plot curves in different colors.

Any use of the replacement operator, however, causes all curves to adopt the final listed color. For example, Plot[vec /. x -> y, {y, -2, 2}, PlotStyle -> {Blue, Red}] gives

How does one specify different colors for different curves if a replacement (/.) is used within the plot command?

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marked as duplicate by Mr.Wizard♦Mar 21 '12 at 0:02

Perfect, thank you. I didn't know about the HoldAll attribute. Having now read about it, if I understand correctly, Hold[x/.x->y] prevents the substitution from taking place. How does Plot manage to plot the curves (incorrect colors aside) over the domain $y\in\left[-2,2\right]$ if the substitution $x\mapsto y$ never takes place? –  user001 Mar 20 '12 at 19:56