private void timer1_Tick(object sender, EventArgs e)//This might work better for you :)
{
Random rand = new Random();
for (int i = 0; i < 255; i++)
{
int A = rand.Next(i);
int R = rand.Next(i);
int G = rand.Next(i);
int B = rand.Next(i);
label2.ForeColor = Color.FromArgb(A, R, G, B);
}
}