Render Model color as Background for texture

Hello,
i got the problem with rendering model with specifying color by user. When user choose color for any part model, and after that apply texture with transparent background on model , colored part will become transparent like on this photo
image
Sorry for my bad english
Update 1: im attaching code what probably doing something wrong

applyTextureToModel(dataURL) {
const textureLoader = new THREE.TextureLoader();
if (dataURL) {
textureLoader.load(dataURL, texture => {
texture.wrapS = THREE.RepeatWrapping;
texture.wrapT = THREE.RepeatWrapping;
texture.repeat.set(1, 1);
if (this.loadedObject) {
const material = new THREE.MeshLambertMaterial({
map: texture,
transparent: true,
color: 0xffffff,
});
material.alphaTest = 0.5;
if (this.loadedObject instanceof THREE.Mesh) {
this.loadedObject.material = material;
this.loadedObject.material.needsUpdate = true;
} else {
this.loadedObject.traverse(child => {
if (child instanceof THREE.Mesh) {
child.material = material;
child.material.needsUpdate = true;
}
});
}
} else {
console.error(“Model not yet loaded.”);
}
});
} else {
console.error(“Data URL is not defined”);
}
}