DAQ slider shading inconsistent with negative range

The two sliders show below are created exactly the same, via the code snipped below (with the exception of the right-most slider having a min value of -5.0 and a max value of 0.0. Why does the right slider shading from [-1.1, 0] not be pure black like the shading for the left slider? How can this be corrected? Can it be corrected in CSS and if so how?

daq.Slider(
    color={
        # "default": 'blue',
        "gradient": False,
        "ranges": {
            "lightgray": [0, 5]
        }
    },
    id='sessionHighlight-max',
    handleLabel={
        'color': params.SLIDER_HANDLE_COLOR,
        "showCurrentValue": True,
        "label": "Tide",
        'style': {
            'fontWeight': 'bold',
            'fontSize': 14
        }
    },
    marks=params.HIGHLIGHT['max'],
    min=0.0,
    max=5.0,
    size=450,
    step=0.1,
    updatemode='mouseup',
    theme={'dark': False},
    value=0.0,
    vertical=True
)