D3D9 DrawPrimitive Gradiente Color - c++

Question

I'm trying to make a color picker system, and for this I need a color gradient.
I'm trying to use DrawPrimitive to draw a square with color vertex. but the result is not what I wanted, the gradient is not so pretty in comparison to other programs
My Gradient:
Gradient Photoshop/ImGui/Other programs seem to:
void GradientColor(float x, float y, float width, float height)
{
static struct D3DVERTEX
{
float x, y, z, rhw;
DWORD color;
};
D3DVERTEX vertices[4];
vertices[0].x = x;
vertices[0].y = y;
vertices[0].z = 0.f;
vertices[0].rhw = 1.f;
vertices[0].color = 0xffffffff; //White
vertices[1].x = x + width;
vertices[1].y = y;
vertices[1].z = 0.f;
vertices[1].rhw = 1.f;
vertices[1].color = 0xffff0000; //Red
vertices[2].x = x;
vertices[2].y = y + height;
vertices[2].z = 0.f;
vertices[2].rhw = 1.f;
vertices[2].color = 0xff000000; //Black
vertices[3].x = x + width;
vertices[3].y = y + height;
vertices[3].z = 0.f;
vertices[3].rhw = 1.f;
vertices[3].color = 0xff000000; //Black
static LPDIRECT3DVERTEXBUFFER9 pVertexObject = NULL;
static void *pVertexBuffer = NULL;
if (!pVertexObject) {
if (FAILED(device->CreateVertexBuffer(sizeof(vertices), 0,
D3DFVF_XYZRHW | D3DFVF_DIFFUSE, D3DPOOL_DEFAULT, &pVertexObject, NULL)))
return;
}
if (FAILED(pVertexObject->Lock(0, sizeof(vertices), &pVertexBuffer, 0)))
return;
memcpy(pVertexBuffer, vertices, sizeof(vertices));
pVertexObject->Unlock();
device->SetStreamSource(0, pVertexObject, 0, sizeof(D3DVERTEX));
device->SetFVF(D3DFVF_XYZRHW | D3DFVF_DIFFUSE);
device->DrawPrimitive(D3DPT_TRIANGLESTRIP, 0, 2);
}
I know the difference is not big, but it's perceptible, Thanks for all.