I would use the pen tool to draw the shape you want to colour, see more on Draw with Pen tools in Photoshop , then when you finished to use the pen tool, change the blend mode from Normal to Color Burn, see the picture. You can learn more here, Blending modes in Adobe Photoshop . This will let you to not do multiple strokes on the brush tool, which it acts like you did duplicate the layer, and this cause the strong colour. You can use the brush tool and change afterwards the Blend Mode
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