Example:
<sheetViews>
    <sheetView tabSelected="1" view="pageBreakPreview" zoomScaleNormal="100" zoomScaleSheetLayoutView="100" workbookViewId="0">
        <selection activeCell="J5" sqref="J5"/>
    </sheetView>
</sheetViews>

Currently, similar conversions should be manually implemented by the users.

Sample method that could be used:

public static Color HexStringToColor(string hexColor)
{
    // Remove the # at the front.
    if (hexColor.StartsWith("#"))
    {
        hexColor = hexColor.Substring(1, hexColor.Length - 1);
    }

    byte a = 255;
    byte r = 255;
    byte g = 255;
    byte b = 255;

    int start = 0;

    // Handle ARGB strings (8 characters long).
    if (hexColor.Length == 8)
    {
        start = 2;
    }

    //Handle contracted RGB strings (3 characters long)
    if (hexColor.Length == 3)
    {
        hexColor = string.Format("{0}{0}{1}{1}{2}{2}", hexColor[0], hexColor[1], hexColor[2]);
    }
    else if (hexColor.Length < 6)
    {
        hexColor = hexColor.PadLeft(6, '0');
    }

    // Convert RGB characters to bytes.
    r = byte.Parse(hexColor.Substring(start, 2), NumberStyles.HexNumber);
    g = byte.Parse(hexColor.Substring(start + 2, 2), NumberStyles.HexNumber);
    b = byte.Parse(hexColor.Substring(start + 4, 2), NumberStyles.HexNumber);

    return Color.FromArgb(a, r, g, b);
}

Provide ability for working with comments in a spreadsheet document.

In Office 365 there are two types of comments:

1. Comments/Notes
2. Threaded Comments 

This item applies to Threaded Comments only.

For Notes, please follow: SpreadProcessing: Provide API for Insert / Delete Comments (Notes)

With the current implementation, the Notes support only a rectangular shape.

Examples:

SpreadProcessing: Upon export, sheet reference in formulas such as VLOOKUP is lost when using whole row/column references.
For example the formula
=VLOOKUP("test",Sheet1!A:C,1,0) is exported as

=VLOOKUP("test",A:C,1,0)

The values applied to the row/column should be explicitly set on each used cell as well. Otherwise, if they are applied on row/column only, the used cells don't use the desired values when opening the document.

To reproduce:

1. Set some content on cell A1
2. Create a row selection and apply a fill color to it (or any other property)
3. Export the document and open it in an application

Observed: All cells except A1 have the specified color.

Workaround: Use cell selection, e.g.:

sheet.Cells[0,10].SetFill(PatternFill.CreateSolidFill(Colors.Red));