How do I quickly change the colour of certain pixels across an image?

[kicka11]

I have large images with pixel shapes (representing cells) and each cell type has a certain colour (6 in total, plus black background). 

I need to rapidly colour-test different colours to find the best combination for visibility. 

I have not been able to find a solution anywhere, as most such approaches are about defining a recognisable shape and then altering colours - this is about changing many 'cells' across a large image in one go. 

Thanks

[user_0815]

Two ways I am aware of:

1 - Menu Select > Select colour… (the bottom one in that section). Now click and drag on the colour you want to select. All pixels of the colour will be in an actual selection with those marching ants. Now use any adjustment layer you prefer to change the colour.

2 - Use an HSL adjustment and use the colour picker. Click on one of the solid colours below the colour wheel and use the picker to set it to that colour which you want to change. Then dial in the colour you want it to be via the slider. Move those 4 control points inside the wheel to narrow down/feather the selected colour.

[kicka11]

@user_0815thanks so much for taking the time. I think both approaches seem to partially work, but ideally i need to change the colours to a specific HEX code. This doesn't seem to be possible with HSL alteration. 

Do you mind explaining exactly how I would do that with the first approach, after I have selected the colours? I click 'apply' but then I can't find a way to actually change to a specific colour. Thanks again

[walt.farrell]

If you can make a good pixel selection of all of them, then you could set the color you want in the Color panel, choose an appropriate brush like a basic round brush, set a large brush size, and paint over the entire canvas. It would be limited to your selection.

[carl123]

28 minutes ago, kicka11 said:

Do you mind explaining exactly how I would do that with the first approach, after I have selected the colours? I click 'apply' but then I can't find a way to actually change to a specific colour.

After making the selection just use Edit > Fill and select the (Hex) colour you want

[David in Яuislip]

Put your blobs on separate layers then put a fill layer inside each so that can be changed as desired to specific hex values

HexBlobs.afphoto

[user_0815]

2 hours ago, kicka11 said:

@user_0815thanks so much for taking the time. I think both approaches seem to partially work, but ideally i need to change the colours to a specific HEX code. This doesn't seem to be possible with HSL alteration. 

Do you mind explaining exactly how I would do that with the first approach, after I have selected the colours? I click 'apply' but then I can't find a way to actually change to a specific colour. Thanks again

With the HSL Method I don't know a precise way. Only a work-around by using the "Info" panel. Place a sample point on the blob and read what HEX colour it is. Change the HSL slider until it matches what you need.

With the second method I would do it non-destructively like this:

1. select the colour like you did. Klick Apply.

2. Create a new FILL-layer: Menu Layer > New Fill Layer and then hit the Mask icon. (With this, you can change this later very quickly.)

3. Click on the fill layer and apply the colour you need in the Colour panel.

You can skip number 2. if you only want to change the colour once. However, with a new layer you can change the colour later much quicker because you don't need to do the selection (1.) again.