Different colors when comparing Plot3D V9 and V10

An alternative to @Rahul's suggested fix:

Plot3D[Sin[x+y^2],{x,-3,3},{y,-2,2}, PlotTheme->{"Classic","ClassicLights"}]

The associated Lighting setting matches the one in Rahul's post:

 "DefaultLighting"/.(Method /.Charting`ResolvePlotTheme["ClassicLights", Plot3D])
 (* {{"Ambient", RGBColor[0.312, 0.188, 0.4]},
     {"Directional", RGBColor[0.8, 0, 0], ImageScaled[{2, 0, 2}]}, 
     {"Directional", RGBColor[0, 0.8, 0], ImageScaled[{2, 2, 2}]}, 
     {"Directional", RGBColor[0, 0, 0.8], ImageScaled[{0, 2, 2}]}} *)

Update: Few more combinations of options that give the same result:

Plot3D[Sin[x + y^2], {x, -3, 3}, {y, -2, 2}, PlotTheme -> "Classic", Lighting -> "Classic"]
(* thanks: Algohi *)

Plot3D[Sin[x + y^2], {x, -3, 3}, {y, -2, 2}, Lighting -> "Classic", PlotTheme->None]

It quite possible that the default lighting has not changed, but that PlotTheme -> "Classic" introduces an explicit color function. That would make a difference because as it says under Lighting in the docs:

Lighting->Automatic uses ambient light together with four light sources fixed relative to the final displayed image. With the typical default setting ColorFunction->Automatic, colored light sources are used; if an explicit setting for ColorFunction is given, the light sources are taken to be white. »

Further, PlotTheme says that "Classic" is a

historical design of plots to remain compatible with existing uses

Note "compatible", not "identical".