Filling and colouring

Perhaps you're looking for something like this:

Plot[{
  ConditionalExpression[x^2, x < 1],
  ConditionalExpression[x^2, x > 1],
  ConditionalExpression[2 + 2 x^2, x < 1]
  },
 {x, 0, 2},
 Filling -> {1 -> Bottom}
 ]

threshold = 1.;

Plot[{x^2, x^2/6, ConditionalExpression[0, x <= threshold]}, {x, 0, 2}, 
 PlotStyle -> {Automatic, Orange, None}, 
 Filling -> {2 -> {{3}, {None, LightOrange}}},
 PlotRange -> {0, 1}]

and

Plot[{x^2, x^2/6, Boole[x > threshold ]}, {x, 0, 2},
 Exclusions -> {{threshold }},
 PlotStyle -> {Automatic, Orange, None}, 
 Filling -> {2 -> {{3}, {None,LightOrange}}},
 PlotRange -> {0, 1}]