How to make a " homogeneous" gradient in glsl?

I don't know what is the best description for my target effect, but I want it to look this:

I made these two attempts, where the color around diagonal line is more close to the right-down vertex.

<img src="https://i.stack.imgur.com/CBuSQ.jpg" width="300" height="300">
<img src="https://i.stack.imgur.com/GbCAJ.jpg" width="300" height="300">

#version 450

layout(binding=0) uniform UniformBufferObject {
    mat4 model;
    mat4 view;
    mat4 proj;
} ubo;

layout(location=0) in vec2 inPosition;
layout(location=1) in vec3 inColor;
layout(location=2) in vec2 inUV;

layout(location=0) out vec3 fragColor;

vec3 azure = { 0.0f, 0.5f, 0.5f };
vec3 blue = { 0.0f, 0.0f, 1.0f };
vec3 green = { 0.0f, 1.0f, 0.0f };

float translate(float i) {
    return i + 0.5;
}

float helpfunc(int x) {
    return mix(mix(blue[x], green[x], translate(inPosition.y)), mix(azure[x], azure[x], translate(inPosition.y)), translate(inPosition.x));
}

void main() {
    gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition, 0.0, 1.0);
    fragColor = vec3(helpfunc(0), helpfunc(1), helpfunc(2));
} 

I thought that this might be leaded by the color space, yet since after exchanging the position of blue and green in function helpfunc, the color of the distinctive diagonal line changed, not the distinctive diagonal line postion. I guess the problem is in algorithm, but I can't figure out what it is or how to solve it.

thks to krOoze, i find a way to solve my problem, since idk if it is the best solution.
the only thing i do is put the step "calculate the color" from vertex shader into frag shader.
here's my code:

//vertex shader
#version 450

layout(binding=0)uniform UniformBufferObject{
    mat4 model;
    mat4 view;
    mat4 proj;
    
}ubo;

layout(location=0)in vec2 inPosition;
layout(location=1)in vec3 inColor;
layout(location=2)in vec2 inUV;

layout(location=0)out vec2 outPosition;

void main(){
    gl_Position=ubo.proj*ubo.view*ubo.model*vec4(inPosition,0.,1.);
    outPosition=inPosition;
}
//frag shader
#version 450

layout(location=0)in vec2 outPosition;

layout(location=0)out vec4 outColor;

vec3 red={1.f,0.f,0.f};
vec3 blue={0.f,0.f,1.f};
vec3 green={0.f,1.f,0.f};
vec3 white={1.f,1.f,1.f};

float translate(float i){
    return i+.5;
}
float helpfunc(int x){
    return mix(mix(blue[x],green[x],translate(outPosition.y)),mix(white[x],red[x],translate(outPosition.y)),translate(outPosition.x));
}
void main(){
    outColor=vec4(helpfunc(0),helpfunc(1),helpfunc(2),1.);
}

and here is my outcome :