Using a shader messes up my alpha in XNA

I'm making a 2D game that ends up being too dark on some laptops, so I figured I'd use a shader so people could brighten it up if need be. Unfortunately, once I got it in there nothing would fade in or out, they'd just pop in and out.

Here's my FX file

float intensity;sampler TextureSampler : register(s0);float4 Glow(float2 texCoord:TEXCOORD0):COLOR0{    float4 Color;    Color = tex2D(TextureSampler, texCoord.xy);    Color.rgb *= intensity;    return Color;}technique Technique1{    pass Glow    {        PixelShader=compile ps_2_0 Glow();    }}

Even after commenting out the Color.rgb *= intensity; line it still removes all fading effects.

I'm using the sprite batch to draw, and I begin and end it a few times because I use different BlendStates

brightnessShader.Parameters["intensity"].SetValue(brightness);spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.AlphaBlend, null, null, null, brightnessShader, Matrix.CreateScale(scale));...spriteBatch.End();spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.Additive, null, null, null, brightnessShader, Matrix.CreateScale(scale));....spriteBatch.End();spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.AlphaBlend, null, null, null, brightnessShader, Matrix.CreateScale(scale));...spriteBatch.End();    

I'm using XNA 4.0.