Your English seems to be completely fine to me, but if it makes you feel more comfortable you can ask questions in Polish – it is understandable for me to a little degree, and I can always use translators as well (I will answer in English, though, to avoid any extra confusion associated with me not using the language correctly).
Don’t worry about it, I genuinely appreciate any activity here, and sure, you can customize colors in the template. For the main text color you need to edit this line in the Styling tab when editing the template:
To find the code of a color you’d like the text to have you can use tools such as this one: Color Picker — HTML Color Codes the value that you need is at the top-left next to the word HEX:
All you need is to copy the value (including # symbol) and paste it after the --mem-text variable as shown above.
If you want to highlight individual words on specific cards, instead of the template in general, you can simply use Anki editing tools. If you open the card browser and select a card you want to edit all standard text formatting options, including highlighting and coloring the words, will be there:
(this is for the desktop version, there are ways to do this on Android too. They are more tricky, but I can provide instructions for that as well if you are interested)
I’m not exactly sure, what happened there. The answer is supposed to be shown at the top of the info screen:
Was it working for you like this before you edited the template? Also, does it happen on all of the other cards as well?
I know it’s not the main point, but if the short interval bothers you, it can easily be increased.