How can you add white noise of a specified magnitude to a colored image?

How can you add white noise of a specified magnitude to an RGB image? I am trying to use imnoise on each individual channel, but I feel like that will produce colored noise. Is that true, or should it come out white? Also, I am using a slider and my range is way off for the magnitude (-255 to 255). What is a suitable range?

Here is what I have at the moment:

val2 = noiseadditiondropdown.Value;
                    if size(image2,3)==3
                       redchannel = image2(:,:,1);
                       greenchannel = image2(:,:,2);
                       bluechannel = image2(:,:,3);
                       
                        switch val2
                            case 2 %White noise addition
                                redchannel = image2(:,:,1);
                                greenchannel = image2(:,:,2);
                                bluechannel = image2(:,:,3);
            
                                noisyredchannel = imnoise(redchannel,'gaussian',whitenoiseslider.Value);
                                noisygreenchannel = imnoise(greenchannel,'gaussian',whitenoiseslider.Value);
                                noisybluechannel = imnoise(bluechannel,'gaussian',whitenoiseslider.Value);
                    
                                image1(:,:,1) = noisyredchannel;
                                image1(:,:,2) = noisygreenchannel;
                                image1(:,:,3) = noisybluechannel;
                    
                                axes(axes1);
                                imshow(image1);