Problem selecting transparent color

[ArthurFfox]

Hello, I've been using Affinity Photo for about 2-3 weeks now to work on a local client's comic book and I am extremely impressed with the efficiency with the program thus far! However I ran into a problem when attempting to remove the blue guide lines (margins used in comic book coloring). These lines are traditionally color coded blue, so that they're "easier" to erase while in a photo editing software and with Photoshop I had no problems erasing them. However I have tried multiple selection options with Affinity but all the magic wand does is either select everything else including the black or selects individual blue pixels and not the blue lines entirely. The blue itself is slightly transparent so that might be an issue?  

Here is what I did to get to this stage if it helps:

Filters > Color > Erase white paper

CTRL + J > CTRL+ E (to make the marker lines darker and then I just merged them together)

Magic Wand tolerance set at 0%.

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I mean I could always erase with a layer mask, but I would prefer a cleaner way to select and erase the blue in one go. Any thoughts?

[Dazzler]

You might find Select > Alpha range > Select Partially Transparent and then delete works here if the bats are completely opaque.

[Dazzler]

Alternatively, the Select > Select Sampled Color... option when clicked on will give a default selection around most of the items of all colours, however when you then click on a colour on the image it'll sample that colour and select items that are that colour and the tolerance control allows you to expand that range a bit if needs be. You can also keep clicking around in the image area whilst the dialogue is open to select slightly different colours etc.

[ArthurFfox]

Second option worked, thank you! Turns out the layer mask I had was confusing the selection tool, so as soon as I deleted said layer the Sampled Color was able to make the correct selection right away.